Tag Archives: Color

The color purple is unlike all others, in a physical sense

Our ability to perceive color is nothing short of a technical miracle — biologically speaking. But there is one color we can see that isn’t quite like the rest. This color, purple, is known as a non-spectral color. Unlike all its peers it doesn’t correspond to a single type of electromagnetic radiation, and must always be born out of a mix of two others.

A violet rectangle over a purple background. Image credits Daily Rectangle / Flickr.

Most of you here probably know that our perception of color comes down to physics. Light is a type of radiation that our eyes can perceive, and it spans a certain range of the electromagnetic spectrum. Individual colors are like building blocks in white light: they are subdivisions of the visible spectrum. For us to perceive an object as being of a certain color, it needs to absorb some of the subdivisions in the light that falls on it (or all of them, for black). The parts it reflects (doesn’t absorb) are what gives it its color.

But not so for purple, because it is a…

Non-spectral color

First off, purple is not the same as violet, even though people tend to treat them as interchangeable terms. This is quite understandable as, superficially, the two do look very similar. On closer inspection, purple is more ‘reddish’, while violet is more ‘blueish’ (as you can see in the image above), but that’s still not much to go on.

Why they’re actually two different things entirely only becomes apparent when we’re looking at the spectrum of visible light.

Image via Reddit.

Each color corresponds to photons vibrating with a particular intensity (which produces their wavelength). Humans typically can see light ranging from 350 to 750 nanometers (nm). Below that we have ultraviolet (UV) radiation, which we can’t see but is strong enough to cause radiation burns on the beach, DNA damage, and other frightful things. Above the visible spectrum, we have infrared (IR), a type of electromagnetic radiation that carries heat, and which armies and law enforcement use in fancy cameras; your remote and several other devices also use IR beams to carry information over short distances.

The numbers above aren’t really extremely important for our purposes here; they describe the exact colors used for flairs on a subreddit I follow, and the wavelengths noted there will shift slightly depending on the hue you’re dealing with. I left the numbers there, however, because it makes it easier to showcase the relationship between light’s physical properties and our perception of it.

What we perceive as violet is, quite handily, the bit of the visible spectrum right next to that of UV rays. This sits on the left side of the chart above and is the most energetic part of light that our eyes can see (low wavelength means high vibration rates, which mean higher energy levels). On the right-hand side, we have red, with high wavelength / low energy levels.

Going through the spectrum above, you can find violet, but not purple. You may also be noticing that while we talk of ultraviolet radiation, we’re not mentioning ultrapurple rays — because that’s not a thing. Purple, for better or worse, doesn’t make an appearance on the spectrum. Unlike red or blue or green, there is no wavelength that, alone, will make you perceive the color purple. This is what being a ‘non-spectral’ color means, and why purple is so special among all the colors we can perceive.

More than the sum of its parts

If you look at orange, which is a combination of yellow and red, you can see that its wavelength is roughly the average of those of its constituent colors. It works with pretty much every color combination, such as blue-yellow (for green) or red-green (for more orange).

Now, the real kicker with purple, which we know we can get by mixing in red with blue, is that by averaging the wavelengths of its two parent colors, you’d get something in the green-yellow transition area. Which is a decidedly not-purple color.

That’s all nice and good, but why are we able to perceive purple, then? Well, the short of it is “because brain”. Although purple isn’t a spectral color in the makeup of light, it is a color that can exist naturally and in the visible spectrum, so our brains evolved the ability to perceive it; that’s the ‘why’. Now let’s move on to ‘how’. It all starts with cells in our eyes called ‘cones’

CIE colour matching functions (CMFs) Xbar (blue), Ybar (green) and Zbar (red). Image via Reddit.

The chart on the left is a very rough and imperfect approximation for how the cone cells on our retinas respond to different parts of the visible spectrum. There’s three lines because there are three types of cone cells lining our retinas. While reality is a tad more complicated, for now, keep in mind that each type of cone cell responds to a certain color (red, green, or blue).

How high each line peaks shows how strong a signal it sends to our brain for individual wavelengths. Although we only come equipped with receptors for these three colors, our brain uses this raw data to mix hues together and produce the perception of other colors such as yellow, or white, and so on.

The more observant among you have noticed that cone cells that respond to the color red also produce a signal for parts of the visible spectrum corresponding to blue. And purple is a mix of red and blue. Coincidence?! No; obviously.

The thing is, while every color you perceive looks real, they’re pretty much all just hallucinations of your brain. When light on the leftmost side of the spectrum (as seen in the chart above) hits your eye, signals are sent to your brain corresponding only to the color red. Move more towards the middle, however, and you see that both red and green are present. But the end perception is that of yellow, or green.

What happens is that your brain constantly runs a little algorithm that estimates what color things you’re seeing are. If a single type of signal is received, you perceive the color corresponding to it. If a mix of signals is received, however, we perceive a different color or hue based on the ratio between signals. If both green and red signals are received, but there’s more of the red than the green, our brains will tell us “it’s yellow”. If the signal for green is stronger than that for red, we see green (or shades of green). The same mechanism takes place for all possible 9 combinations of these colors.

That bit to the right of the chart, where both red and blue signals are sent to the brain, is where the color purple is born. There’s no radiation wavelength that carries purple like there is with violet or orange. The sensation of purple is created by our brains, sure, but the reason why it needs to be created in the first place is due to this quirk of how the cone cells in our eyes work. From the chart above you can see that cells responding to green pigments also show some absorption in the area corresponding to purple, but for some reason, our brains simply don’t bother with it.

From my own hobbies (painting) I can tell you that mixing violet with green produces blue, but mixing purple with green results in brown. Pigments and colored light don’t necessarily work the same way, this is all anecdotal, and I have no clue whether that’s why green signals get ignored in purple — but I still found it an interesting tidbit. Make of it what you will.

In conclusion, what makes purple a non-spectral color is that there isn’t a single wavelength that ‘carries’ it — it is always the product of two colors of light interacting.

Are there any others like it?

Definitely! Black and white are prime examples. Since there’s not a single wavelength for white (it’s a combination of all wavelengths) or black (no wavelengths), they are by definition non-spectral colors. The same story with gray. These are usually known as non-colors, grayscale colors, or achromatic hues.

Furthermore, colors produced by mixing grayscale with another color are also considered non-spectral (since one component can’t be produced by a single wavelength, the final color can’t be produced by a single one either). Pink is most often given as an example, as is brown, since these can be produced using non-spectral colors (white and/or purple for pink, gray/black for brown).

Metallic paints also, technically, are non-spectral colors. A large part of the visual effect of metallic paints is given off by how they interact with and scatter light. A certain wavelength produces a single color; the shininess we perceive in metallic pigments can’t be reproduced using a single wavelength, as this is given off by tiny variations in surface reflecting light in different directions. The metal itself may well be a solid color, but our final perception of it is not. A gray line painted on canvas doesn’t look like a bar of steel any more than a yellowish one can pass off as a bar of gold. As such, metallic colors are also non-spectral colors.

Why blue and green are the brightest colors in nature

Throughout nature, the colors of blue and green are usually the brightest and most intense. A group of researchers from Cambridge University has now figured out the reason why, after they performed computational modeling to get to the bottom of things.

Credit Flickr Mathias Appel

Physicist Gianni Jacucci and his team worked on a numerical experiment, assessing the ranges of matt structural color. This is a phenomenon responsible for some of the most intense colors in nature. The model showed how this intensity effect extends only as far as blue and green within the visible spectrum. Notably, matt structural coolers cannot be recreated in the red region of the visible spectrum.

“Most of the examples of structural color in nature are iridescent — so far, examples of naturally-occurring matt structural color only exist in blue or green hues,” said co-author Lukas Schertel in a statement. “When we’ve tried to artificially recreate matt structural color for reds or oranges, we end up with a poor-quality result, both in terms of saturation and color purity.”

Structural color is formed from the disordered array of structures in a way that results in angle-independent matt colors, meaning the colors look the same from any viewing angle. The basis of structural color, the researchers found, is not the result of pigments or dyes, such as with the glossy yellow of the buttercup, which is achieved through a yellow carotenoid pigment.

In contrast, the coloration seen on the wings of birds and butterflies and on insects, for example, is the result of internal structure alone. The way a color manifests itself is due to the way that structures are arranged at the nanoscale, reflecting light in complex patterns.

Jacucci hopes the data will prove useful with the development of non-toxic paints or coatings with intense color that never fades. Nevertheless, it will take some time for this to happen, as the researchers have to figure out the limitations for recreating these types of colors. They plan to investigate further the use of other kinds of nanostructures to overcome the limitations.

“In addition to their intensity and resistance to fading, a matt paint which uses structural color would also be far more environmentally-friendly, as toxic dyes and pigments would not be needed,” said in a statement first author Gianni Jacucci from Cambridge’s Department of Chemistry.

The study was published in the journal PNAS.

How on Earth did we start using “once in a blue moon”?

You’ve heard it, I’ve heard it, but not many people we know have actually seen a blue moon — so what gives?

Am image of the moon captured through a blue filter.
Image credits steviep187 / Flickr.

“Once in a blue moon” refers to events that only happen very rarely, but it’s a tricky idiom. It doesn’t refer to a moon that’s actually blue, although it can appear to be that color under certain conditions and that probably shaped the saying.

A blue moon is a real occurrence and, you might be surprised to hear, isn’t actually that rare or unpredictable. Blue moons are ‘extra’ full moons of the regular gray color that pop up every two or three years due to misalignment in the lunar and solar circle. But the phrase was first used to refer to something being absurd — like someone arguing that the moon is blue.

So let’s take a look at both halves of this idiom and see why they came to represent the quintessential rare occurrence.

The literal blue moon

Image credits Bobby Jones.

The moon can naturally appear blue or light-blue in the sky. It’s a rare event caused by the presence of dust or smoke particles in the atmosphere at night which alter the way light is diffracted in the atmosphere. If these particles are of the right size, they can scatter the red part of the light spectrum, leaving the rest untouched.

Because visible light spans from red (low-energy) to blue (high-energy), this scattering makes everything take on a blue tint. Since the moon is a white-ish gray on a dark background, this effect causes it to look blue.

This type of blue moon is probably what spawned the idiom. It’s very rare and very unpredictable, as its appearance relies directly on phenomena such as massive wildfires or volcanic eruptions. The fact that it’s entirely dependent on local phenomena also means blue moons are only visible from relatively small areas at a time, not globally — which compounds their rarity.

Some events that led to blue moons include forest fires in Canada, and the eruptions of Mount St. Helens in 1980 and the El Chichón volcano in Mexico in 1983. The eruption of Krakatoa in 1883 (one of the largest in history) reportedly caused blue moons for nearly two years.

A pretty exciting implication of the mechanism that spawns blue moons is a purple sun. In 1950, as huge fires swept the bogs of Alberta, Canada billowing with smoke, leading to sightings of blue moons from the US to England the following night. Two days later, reports of an indigo sun peering through the smoky skies also started to surface.

File:Blood moon 73.jpg
A blood moon.
Image credits Andrey73RUS / Wikimedia.

So why don’t all volcanic eruptions and wildfires turn the moon blue? Well, the size of ash or oil/tar particles they generate is very important. These have to be wider than the wavelength of red light, which is 0.7 micrometers, to block these rays. At the same time, very few to no particles of smaller sizes should be present, as these would help scatter other colors and destroy the overall effect.

Naturally-occurring ash tends to be a mix of particles of various sizes, with most being smaller than the above threshold. Since smaller particles preferentially scatter (i.e. remove) light towards the high end of the spectrum (blue), natural ash clouds typically give everything a shade of red. Red or blood moons are thus a much more common occurrence than blue moons.

The figurative blue moon

Traditionally a blue moon is an additional full moon that appears every 2 and a half years or so, according to NASA. In recent times it has also come to denote the second full moon to appear within a single calendar month in popular use.

This stems from the way lunar and solar cycles relate to one another. There are 29.5 days between full moons, the agency goes on to explain, so each year will have roughly 12.3 full moons. Another implication of this is that 28-days-long February can’t ever have a blue moon.

Both uses of the phrase are considered valid today.

Over time, the idiom turned from meaning that something is impossible to “never” — think along the lines of “I’ll help you when the pigs fly”.

“The definition of a Blue Moon [as] ‘the second full moon in a calendar month,’ is a curious bit of modern folklore. How it emerged is a long story involving old almanacs, a mistake in Sky and Telescope magazine, and the board game Trivial Pursuit,” wrote Dr. Tony Phillips for NASA.

One of the almanacs Dr. Phillips mentions is the Maine Farmer’s Almanac, more specifically its August 1937 issue. The publication followed certain conventions about how to name each moon depending on the time of year. The first full moon of spring for example was called the Egg Moon, Easter Moon, or Paschal Moon, and had to fall within the week before Easter. If a particular season had four moons, the extra one was called a Blue Moon to maintain the naming conventions.

The definition of the blue moon as being the second full month in a single month came, according to Space, from a mistaken interpretation of the term which was popularized by a nationally syndicated radio program in 1980.

Rarer than Blue Moons are double Blue Moons — when the same calendar year gets two of these events. They’re much rarer, only occurring about 3-5 times every hundred years or so; the next double blue moons are expected in 2037. As for a single blue moon, the next one is expected on October 31, 2020.

MIT develops programmable, color-changing dyes that you can spray on basically anything

If you’ve ever been envious of chameleons, rejoice! New research is bringing their color-changing properties to a dye near you.

Image credits Yuhua Jin et. al, 2019.

Researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have designed a new, reprogrammable ink that can change color when exposed to ultraviolet (UV) and visible light sources. Dubbed “PhotoChromeleon,” the dyes can be used on anything from phone cases to cars and is resilient enough to be used in natural environments without rubbing off.

Color, changed

“This special type of dye could enable a whole myriad of customization options that could improve manufacturing efficiency and reduce overall waste,” says CSAIL postdoc Yuhua Jin, the lead author of the new study.

“Users could personalize their belongings and appearance on a daily basis, without the need to buy the same object multiple times in different colors and styles.”

PhotoChromeleon dyes are a mix of photochromic dyes that can be sprayed or painted onto the surface of any object to change its color. The process is fully reversible and can be repeated infinitely, the team explains.

The dye comes as a further development of the team’s previous “ ColorMod,” a process that involves the use of 3-D printers to fabricate items that can shift their color. PhotoChromeleon comes to address several of the limitations of ColorMod that the authors weren’t very happy with — namely, it’s limited color scheme and low-resolution results.

ColorMod relies on individually-printed 3-D pixels, and there’s a limit to how small they can be built. Overall, this makes the resolution of the finished product feel a bit grainy. As far as the colors are concerned, these pixels can only shift between two states, one showing its original color, and a transparent one. Again, cool, but not as cool as it could be.

The team’s work definitely paid off, however. They explain that PhotoChromeleon ink can be used to create anything from a landscape to zebra patterns to a flame pattern using a larger palette of colors.

PhotoChromeleon is made by mixing cyan, magenta, and yellow (CMY) photochromic dyes (i.e. dyes that change color when exposed to light) into a sprayable solution. By understanding how each dye interacts with different wavelengths, the team can control each color channel by activating and deactivating them with the corresponding light sources.

More specifically, they use three different types of light with different wavelengths to ‘eliminate’ each of the primary colors. For example, blasting the dyes with blue light would inactivate the yellow color (it’s chromatic opposite), leaving only magenta and cyan which gives an overall blue appearance. Blast it with a green light and it would turn blue (by inactivating the magenta dye).

“By giving users the autonomy to individualize their items, countless resources could be preserved, and the opportunities to creatively change your favorite possessions are boundless,” says MIT Professor Stefanie Mueller.

Using the dyes is as simple as spraying it over an object, then placing it in a box with a projector and UV light. The UV light first ‘saturates’ the dyes, turning them from transparent to visible, and the projector ‘desaturates’ them as needed (this produces the final color or color patterns). To reset the whole lot, all you have to do is blast it again with UV light and start over.

In order to help you get the exact finish you want, the team also developed a user interface to process designed and patterns for projection onto the desired items. Users can upload a blueprint and the program handles mapping (i.e. bending and applying it) onto the object.

As proof-of-concept tests, the team used their dye on a car model, a phone case, a shoe, and (quite fittingly) a small toy chameleon. Depending on the shape and orientation of the object, the process took between 15 to 40 minutes, the patterns all had high resolutions and could be successfully erased when desired.

While PhotoChromeleon is definitely more capable than its predecessor, it’s not perfect. The team didn’t have access to photochromic dyes that perfectly match magenta or cyan, so they used close approximations. In the future, they plan to collaborate with materials scientists to improve their dyes.

The paper “Photo-Chromeleon: Re-Programmable Multi-Color Textures Using Photochromic Dyes” has been published in the Proceedings of UIST 2019.

Why is snow white?

Every time it snows, the world turns white, even for the briefest of moments. Today we’re taking a look at why that is.

Snow street.

Image via Pixabay.

You likely hear the song “White Christmas” played every time the winter holidays swing around. It goes to show just how deep cultural associations between snow and its color — that striking, pure, sparkling white — run. If you think about it, however, something doesn’t add up. Snow is basically made up of tiny crystals of water (ice) caked one on top of the other. Water isn’t white; nor is ice, for that matter.

Logic dictates that there must be another element coming into the mix to make snow, well, snow-white. There is. To whet your appetite, it’s basically the same process that makes polar bears appear white. So let’s see what it is.

Color me surprised

To get a clearer picture of why snow appears white, we need to take a look at what generates color in the first place.

Our eyes are basically sensors designed to pick up on a particular spectrum of electromagnetic radiation — which, surprise, surprise, we call the ‘visible light’ spectrum. We perceive different wavelengths or intervals of this spectrum as different colors: ‘wider’ waves look red to us, while ‘narrower’ waves appear to be blue.

Light is pretty much like any other type of radiation. When it hits an object, it can pass through, interact with it, or be reflected completely. Objects take on different colors because their individual building blocks (atoms or molecules) vibrate in response to different frequencies of energy (such as that carried by light). They absorb a particular band of energy to sustain this vibration — which transforms it to heat. The light frequencies which don’t get absorbed can keep going through this material (which makes it transparent or translucent) or get reflected (making the material opaque).

What you see as ‘color’ is the blend of all energy intervals or bands from the visible spectrum that a material doesn’t absorb. Think of white light as a sum of all the colors canceling each other out. To get a particular shade, then, you need to do one of two things. You can subtract its opposite, which we call its ‘complementary’ (here’s a handy color wheel), from the mix, leaving that particular color ‘uncanceled’. Alternatively, you can absorb all other wavelengths and reflect only the color you want.

As an example, leaves appear to be a fresh green because chlorophyll absorbs the wavelengths corresponding to red and blue. Their complementary colors are green and orange/yellow. Leaves absorb only a fraction of the green wavelengths, and what’s reflected creates their color. It’s particularly interesting to note that sunlight is heavy in the green-wavelengths of light. Plants want red and blue light because they’re the less energetic parts of solar radiation. Going for the green spectrum would actually radiation-fry the leaves’ biochemical gears.

Don’t judge a snow by its color

If you put a chunk of ice next to a handful of snow, it’s pretty easy to tell that their colors do not match. One looks basically like solid water while the other is all glimmery, white, and definitely not transparent. So what gives?

Well, first off, caution to the wise: ice isn’t transparent — it’s translucent. Some of the atoms in the ice molecule are close enough to alter lightwaves as they come into contact. Think of it like the light having to squeeze between these atoms as it passes through ice. It doesn’t bother the light very much, but it does ‘bend’ its trajectory a little. Put your finger in a glass of water, and the submerged part will look skewed compared to the rest of your hand; it’s the same process at work.

Shape and size also make an appearance here. Snow is made up of many tiny ice crystals stacked together. When light encounters snow, it goes through the first layer of crystals and gets bent a little. From here, it passes to a new crystal, and the process repeats. Kind of like a disco ball, the snow keeps refracting light until it’s bent right out the pile. Since ice is translucent (doesn’t absorb any wavelength of light), the color of this light isn’t altered, so it’s still white when it exits the pile of snow to hit your retina.

Powder snow.

Matte but glittery.
Image via Pixabay.

The small size of ice crystals in snow also gives it that ‘matte but glittery’ look. Smooth objects reflect light specularly, or like a mirror. Rough surfaces scatter the light they reflect instead, which is why we can perceive texture from looking at an object. The crystals in snow are smooth, so each reflects light specularly. From the right angles, you can see this as tiny, bright reflections on the ice. When clumped up together, however, the crystals scatter light overall. Because the way light falls on it helps create the color, snow can take shades of blue, purple, or even pink in certain circumstances — when it’s in shadow, for example.

As for the polar bears, they’re not really white. Their fur is actually pretty dark in color. Polar bears’ coats are made of two layers of hairs, one short and thick, the other a bit longer and more sparse. This second, longer coat is made up of transparent hairs with hollow interiors. Much like in the case of snow, light falling on these hairs scatters (thanks to light-scattering particles inside the hollow cores) and is reflected back out, giving the bears a white appearance. Salt particles in between the hairs left over from ocean water evaporating after a swim further enhance this effect.


Climate change will recolor much of the oceans by 2100, MIT research suggests

Climate change might be changing the oceans’ color in the future, new research reveals.


Image credits Dimitris Vetsikas.

Significant changes to global phytoplankton populations and their distributions in the coming decades will intensify the oceans’ blues and greens, new research from MIT suggests. These changes should be observable from orbit, the authors add, meaning satellites could be used as an early warning system against wide-scale changes in marine ecosystems.

Blue-green algae

The team reports developing a global model which simulates the growth rate and interactions between different species of phytoplankton (bacteria and single-cell algae). This model allowed them to estimate how the mix of phytoplankton species will evolve in various locations throughout the world as temperatures rise in the future.

The team also simulated how phytoplankton absorb and reflect light, and estimates a perceivable change in the ocean’s color as global warming affects the makeup of phytoplankton communities.

“The model suggests the changes won’t appear huge to the naked eye, and the ocean will still look like it has blue regions in the subtropics and greener regions near the equator and poles,” says lead author Stephanie Dutkiewicz, a principal research scientist at MIT’s Department of Earth, Atmospheric, and Planetary Sciences and the Joint Program on the Science and Policy of Global Change.

“That basic pattern will still be there. But it’ll be enough different that it will affect the rest of the food web that phytoplankton supports.”

Falkland Islands phytoplankton bloom.

An example of how phytoplankton can change ocean color. Picture taken off the coast of the Falkland Islands, 2015.
Image credits NASA via Wikimedia.

The team allowed their model to simulate conditions up to the end of the present century. By the year 2100, they report, over 50% of the world’s oceans will suffer shifts in color due to climate change. Areas that are predominantly blue, such as the subtropics, will become even more blue as phytoplankton — and all the life it supports, which is virtually all life in the area — dwindle. Greener areas, such as those near the poles today, may turn deeper shades of green as warmer temperatures cause blooms of phytoplankton.

Ocean color is formed by the interaction between light, water, and whatever is in the water. H2O itself absorbs most of the light spectrum except for part of the blue wavelengths — which get reflected. That’s why relatively-pure oceans or other bodies of water look blue from space. Organisms in the water tend to change this overall color, as they absorb and reflect different wavelenghts of light.

Based on this principle, scientists have been using satellites to measure ocean color since the late 1990s. This data can be used to estimate the amount of chlorophyll in a given ocean region, and by extension the amount of phytoplankton. But Dutkiewicz says chlorophyll estimates don’t necessarily reflect climate change — significant swings in chlorophyll could come down to global warming, but they could also be due to “natural variability” due to natural phenomena such as weather.

“An El Niño or La Niña event will throw up a very large change in chlorophyll because it’s changing the amount of nutrients that are coming into the system,” Dutkiewicz says. “Because of these big, natural changes that happen every few years, it’s hard to see if things are changing due to climate change, if you’re just looking at chlorophyll.”

Phytoplankton bloom swirly.

A particularly-swirly Phytoplankton bloom off the coast of South Africa, near where the South Atlantic meets the Southern Indian Ocean.
Image credits Flickr / NASA Goddard Space Flight Center.

So the team looked to satellite measurements of reflected light, instead. They started with a computer model used previously to predict phytoplankton changes caused by rising temperatures and ocean acidification. This model takes information about phytoplankton, such as feeding and growth patterns, and incorporates it into a physical model that simulates the ocean’s currents and mixing. However, this time they also gave the model the ability to estimate the specific wavelengths of light absorbed and reflected by the ocean, depending on the amount and type of organisms in a given region.

“Sunlight will come into the ocean, and anything that’s in the ocean will absorb it, like chlorophyll,” Dutkiewicz says. “Other things will absorb or scatter it, like something with a hard shell. So it’s a complicated process, how light is reflected back out of the ocean to give it its color.”

The model’s results were compared to actual measurements of ocean-reflected light taken in the past. The two data sets matched well enough to suggest the model can be used as an accurate predictor of ocean color in the future, the authors write.

So the team allowed the model to work after setting mean temperatures to rise by up to 3 degrees Celsius up to 2100. This increase is consistent with most estimates of how climate conditions will fluctuate under a business-as-usual scenario. Blue and green wavelengths responded the fastest under this scenario, the researchers report. They add that these wavelengths also show a significant shift, due specifically to climate change, much earlier than previously predicted climate-change-induced changes in chlorophyll by 2055.

“Chlorophyll is changing, but you can’t really see it because of its incredible natural variability,” Dutkiewicz says. “But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites. So that’s where we should be looking in satellite measurements, for a real signal of change.”

According to their model, climate change is already changing the makeup of phytoplankton, and by extension, the color of the oceans. By the end of the century, they add, we will see “a noticeable difference in the color of 50 percent of the ocean”, with “potentially quite serious” implications. Different hues of chlorophyll absorb different wavelenghts of light, and such climate-induced changes could have a dramatic impact on the ocean’s food webs, the team concludes.

The paper “Ocean colour signature of climate change” has been published in the journal Nature Communications.

Scientists use nano-ink to 3D print color-changing cup

Researchers have built a plastic cup that changes its color and transparency, using gold nanoparticles and 3D printing.

Although they may have not realized it, humans have been using nanotechnology since the Antiquity. Shiny colors in pottery and glass made hundreds and thousands of years ago represent an early usage of nanoparticles — though not many of these ornaments still survive.

The most famous example is probably the Lycurgus cup — a 4th-century Roman glass cage cup made of a dichroic (two-colored) glass, which is red when lit from behind and green when lit from in front. The Lycurgus cup is the only complete Roman object made from this type of glass, and the one exhibiting the most impressive change in color.

This dichroic effect was achieved by including tiny proportions of gold and silver nanoparticles in the glass material. The exact process remains unclear, and it’s not clear if the makers understood or controlled it or if it came as an accident. The quantities of gold and silver are so minute that they may have been included by accident, as a residue in the workshop or on the tools.

Metallic nanoparticles were also used for staining glass during medieval times, the new study reads. Examples of which can still be found in many churches and cathedrals in Europe. Now, researchers have recreated that technique and brought it to the 21st century — using 3D printing.

Vittorio Saggiomo and colleagues from Wageningen University have shown how to fabricate a 3D printable dichroic material using gold nanoparticles, jumping from the 4th century Roman glassmiths’ methods to a modern technology.

The team used a modified version of something called the Turkevich method to create the color-changing coating. The presented synthesis is easy and fast, taking only a few minutes. During this time, the color changes several times, from the initial yellow solution of the gold ions, to a blue about one minute after the addition of another ingredient (a citrate solution). Two minutes later, the solution turns to a deep black color, before ultimately becoming dichroic after two minutes of boiling.

“The time dependent study shows the formation of small gold nuclei that in time cluster together forming nanowire-like structures concomitant to the firstcolor change,” researchers write. “The second change of color, from ink-black to purple, is accompanied by an enhancement of the scattering, giving the purple solution a brown reflection. While boiling, the gold nanowires fragment, creating nanoparticles with a large head and a slim and long tail, comparable to a tadpole. Over time the tail starts to shrink.” Both steps, individually, have been previously studied.

Ultimately, the material is dichroic because the gold particles interact differently with different wavelengths, absorbing some and reflecting the others.
The coating obtained thusly is 3D-printing compatible, and was used for printing plastic “21st century Lycurgus cups”. These particles don’t influence any other physical or chemical characteristics of the cup.
The study was published in ChemRxiv.


Wilson's Bird of Paradise.

Birds-of-paradise males need more than looks to get a girlfriend

Female birds-of-paradise are very picky with their mates, new research shows.

Wilson's Bird of Paradise.

Wilson’s Bird of Paradise (Diphyllodes respublica).
Image credits Serhanoksay / Wikimedia.

Birds-of-paradise didn’t get their name for naught. The males of the species are renowned for their incredible plumage, complex calls, and dazzling dance moves. However, all this fluff isn’t enough to convince the discerning objects of their affections. A new study reports that the female preference may also be tied to where the males ply their courting: on the ground or up in the trees.

Flirts from paradise

Most of the 40 known species of bird-of-paradise live in New Guinea and northern Australia. For the study, the team analyzed 961 video and 176 audio clips retrieved from the Cornell Lab’s Macaulay Library archive. They also drew on 393 museum specimens from the American Museum of Natural History in New York City. Based on this material, they say that certain behaviors and traits are correlated, as follows:

  • The number of colors on a male and the number of different sounds he makes. The more colors he sports, the larger his repertoire.
  • Dance complexity and the number of sounds a male can produce. The most dazzling dancers also have the widest range of sounds they weave into their songs.
  • Males that display in a group (a lek) tend to have more colors. The team believes this helps them stand out better amid the competition, canceling out some of the drawbacks of the lek.

Victoria's riflebird.

A male (black, top) Victoria’s riflebird (Ptiloris victoriae) displays for a female (brown, bottom). Victoria’s riflebirds are also birds-of-paradise, native to northeastern Queensland, Australia.
Image credits Francesco Veronesi / Wikipedia.

According to the study, female preference drives the evolution of physical and behavioral traits that make the species’ males so distinctive. Lead author Russell Ligon says that females evaluate not only how attractive a male is, but also how well he sings and dances. Their preference for certain combinations of traits results in what his team calls a “courtship phenotype” — the phenotype is an individual’s traits determined by both genetics and environment.

Because females pick and choose mates based on a combination of characteristics (rather than a single one), males have had ample opportunity to ‘experiment’ with their courtship displays, the team reports. This led to the large variation seen in the species’ courting behaviors today — if females were looking for a single characteristic, all the males would simply try to double down on it. Of course, it also helps that the birds have few natural predators to interrupt all the romancing.

Female scrutiny may also have a surprising effect: determining whether a male will perform courting behavior on the ground or up in the trees. The researchers say that location matters when selecting the best approach to impress potential mates:

“Species that display on the ground have more dance moves than those displaying in the treetops or the forest understory,” explains Edwin Scholes, study co-author and leader of the Cornell Lab’s Bird-of-Paradise Project.

“On the dark forest floor, males may need to up their game to get female attention.”

Males of species that display above the canopy — where there is less interference from trees and shrubs to block sounds — sing more complex songs. Their dance moves, however, are less elaborate.

The paper has been published in the journal PLOS Biology.

Blood Moon.

What causes Blood Moons? The same thing that makes skies blue

When the Moon turns bloody, it’s Earth at work.

Blood Moon.

Image via Pixabay.

Humanity has always kept an eye on the heavens. Societies lived and died by natural cycles, and these orbs in the sky seemed to dictate the rhythm of life — so they imposed themselves as central players in our mythoi. The imprint they left on our psyche is so deep that to this day, we still name heavenly bodies after gods.

But two players always commanded center stage: the Sun and the Moon. One interaction between the two is so particularly striking that virtually all cultures regarded it as a sign of great upheaval: the blood moon. Its perceived meaning ranges from the benign to the malevolent. Blood moons drip with cultural significance, and we’ll explore some of it because I’m a huge anthropology nerd.

But they’re also very interesting events from a scientific point of view, and we’ll start with that. What, exactly, turns the heavenly wheel of cheese into a bloody pool? Well, let me whet your appetite by saying that it’s the same process which produces clear blue skies. Ready? Ok, let’s go.

The background

Geometry of a lunar eclipse.

The geometry of a lunar eclipse.
Image credits Sagredo / Wikimedia.

For context’s sake, let’s start by establishing that the moon doesn’t shine by itself. It’s visible because it acts as a huge mirror, beaming reflected sunlight down at night. During a total lunar eclipse, the Earth passes between the Sun and the Moon, blocking sunlight from hitting its surface. Blood moons happen during such lunar eclipses. A sliver of light is refracted (bent) in the atmosphere, passing around the Earth and illuminating the Moon. This is what gives it that reddish colo

It all comes down to how light interacts with our planet’s atmosphere, most notably a process called Rayleigh scattering: electromagnetic radiation interacts with physical particles much smaller in size than the radiation’s wavelength.

For context’s sake part deux, what our eyes perceive as white light is actually a mix of all the colors we can see. Each color is generated by a particular wavelength interval (more here).

Boiled down, different bits of light get more or less scattered depending on their wavelength. It’s quite potent: roughly a quarter of the light incoming from the Sun gets scattered — depending on fluctuating atmospheric properties such amount of particles floating around in it — and some two-thirds of this light reaches the surface as diffuse sky radiation.

The Blood Moon

As a rule of thumb, our atmosphere is better at scattering short wavelengths (violets and blues) than long wavelengths (oranges and reds). ‘Scattering’ basically means ‘spreading around’, and this makes the sky look blue for most of the day. This scattering is not dependent on direction (or, in fancy-science-speak, it’s an isotropic property) but its perceived effect is.

When the sun is high in the sky, light falls roughly vertically on our planet; as such, it passes through a relatively short span of the atmosphere. Let’s denote this rough length with ‘a‘.

The light of dawn and dusk arrives tangentially (horizontally) to the planet. It thus has to pass through a much longer span of the atmosphere than it does at noon. Blues become scattered just like in the previous case as light traverses this a distance through the atmosphere. But it then has to pass through yet more air. So greens (the next-shortest wavelengths) also become dispersed. That’s why the sky on dawn or sunsets appear red or yellow (the remaining wavelengths).

Blood Moon.

The same mechanism is at work during a blood moon. Light passing through the Earth’s atmosphere gets depleted in short wavelengths, making it look yellowy-red. This makes the Moon appear red as it reflects red light back to our eyes.

One cool effect of this dispersion is that blood moons sometimes exhibit a blue-turquoise band of color at the beginning and just before the end of the eclipse. This is produced by the light that passes through the ozone layer in the top-most atmosphere. Ozone scatters primarily red light, leaving blues mostly intact.

Cultural meanings

Many ancient civilizations looked upon the blood moon with concern: in their eyes, this was an omen that evil was stirring.

“The ancient Inca people interpreted the deep red colouring as a jaguar attacking and eating the moon,” Daniel Brown wrote for The Conversation. “They believed that the jaguar might then turn its attention to Earth, so the people would shout, shake their spears and make their dogs bark and howl, hoping to make enough noise to drive the jaguar away.”

Some Hindu traditions hold that the Moon turns red because of an epic clash between deities. The demon Swarbhanu tricks the Sun and Moon for a sip of the elixir of immortality. As punishment Vishnu (the primary god of Hinduism) cuts off the demon’s head — which lives on as Rahu.

Understandably upset by the whole experience, Rahu chases the sun and moon to devour them. An eclipse only happens if Rahu manages to catch one of the two. Blood Moons form when Rahu swallows the moon and it falls out of his severed neck. Several things, such as eating or worshiping, are prohibited, as Hindu traditions hold that evil entities are about during an eclipse.

Other cultures took a more compassionate view of the eclipsed moon. The Native American Hupa and Luiseño tribes from California, Brown explains, thought it was wounded or fell ill during such an event. In order to help its wives in healing the darkened moon, the Luiseño would sing and chant healing songs under an open sky.

My personal favorite, however, is the approach of the Batammaliba people, who live in the nations of Togo and Benin in Africa. Their traditions hold that the lunar eclipse is a conflict between sun and moon; we little people must encourage them to bury the hatchet! Such events are thus seen as an opportunity to lay old animosities and feuds to rest;

I’m definitely going to try that during the next blood moon.

Zebra Finch.

Birds perceive colors and hues the same way we do

Zebra finches seem to clump similar hues together and perceive them as single colors, new research suggests. This approach is similar to how the human mind processes color and sheds light on the biological root of color perception.

Zebra Finch.

Zebra finches break the color spectrum into discrete colors — much like we do.
Image credits Ryan Huang / TerraCommunications LLC

For zebra finch (Taeniopygia guttata) males, wooing is all about what colors you’re wearing. These gents sport various hues on their beaks, ranging from light orange to dark red, which they use to attract mates. But all their chromatic efforts might be in vain, new research suggests, as the females may simply not perceive subtle nuances.

Red is red

For the study, the researchers worked with 26 zebra finch females and a handful of paper discs the size of a small coin. Some of these discs were painted in a solid color, while others were two-toned. The birds were taught that flipping over a two-toned disc earns them a reward in the form of a millet seed hidden beneath it. Solid-colored discs, meanwhile, didn’t return any tasty treats.

What the team wanted to determine through this experiment was how well the zebra finches could perceive ranges of hues. A bird picking at a certain disk before others during the experiment indicated that it perceived it as being two-toned, i.e. that it could perceive the hues on the disk as being different from one another. To see exactly how well the birds could distinguish different hues, some trials involved discs painted in color pairs that were far apart on the color spectrum (violet and yellow would be such a combination) while others used colors that were more similar (red-orange, for example).

Perhaps unsurprisingly, the females found it a breeze to perceive pairings of dissimilar colors. However, they didn’t fare nearly as well when trying to discern pairings of the hues in between these colors. The findings suggest a threshold effect at work — a sharp perceptual boundary near the orange-red transition.

The birds were also much better at spotting a two-toned disc if it bore colors from the opposite sides of the boundary (i.e. red-orange, for example) than pairs from the same side (two shades of the same color). This effect persisted even when the pairs were all equally far apart on the color spectrum, the team notes. This suggests that, while the finches have no problem perceiving different colors side-by-side, they do have some difficulty perceiving different hues of the same color on the discs.

First off, the findings help us gain a better understanding of how zebra finches handle romance. Previous research has shown that red-beaked males have more success with the ladies, likely because the color denotes good health. While this present study doesn’t show whether the females prefer one color over another, it does help us understand what females perceive when looking at potential mates.

The findings indicate that the birds lump all hues of red on one side of a certain threshold as being ‘red’. Because of this, the females likely aren’t very picky.

Color wheel.

I give thee the color wheel.
Image credits László Németh.

“What we’re showing is: he’s either red enough or not,” said senior author Stephen Nowicki, a biology professor at the Duke University.

It also helps us gain a better understanding of our own vision. The process of lumping similar hues together and perceiving them as a single color, known as categorical color perception, is something that our brain does as well. It’s not yet clear whether we share the same orange-red threshold with zebra finches, but the fact that we both exhibit categorical color perception suggests that the process has deep biological roots. Color, then, might not be just a construct of human language and culture, but may also stem from biological hardwiring.

Still, it likely doesn’t happen in the eye, the team writes — categorical color perception, even in zebra finches, is probably a product of their minds.

We don’t ‘see’ the light that hits our retina; what we see is the image our brain constructs from that data. This type of color perception, then, could be a way for the brain to help reduce ambiguity and noise from the environment — a way for our lumps of gray matter to help keep images simple so we don’t get overwhelmed.

“We’re taking in this barrage of information, and our brain is creating a reality that is not real,” said senior author Stephen Nowicki.

“Categorical perception — what we show in zebra finches — is perhaps one strategy the brain has for reducing this ambiguity,” adds Duke postdoctoral associate and paper co-author Eleanor Caves. “Categories make it less crucial that you precisely interpret a stimulus; rather, you just need to interpret the category that it’s in.”

The paper “Categorical Perception of Colour Signals in a Songbird” has been published in the journal Nature.

Ankle x-ray color.

Color X-Ray imaging is just around the corner — and we have the photos to prove it

After 10 years of research and development, one company has now unveiled the first-ever color X-ray scanner.

Mars Bioimaging.

Image credits MARS Bioimaging.

The boring old black-and-white X-ray slides are a thing of the past — after 10 years spent in development, MARS Bioimaging has unveiled the first-ever color X-ray scanner. The device offers physicians an unprecedented tool to peer into the bodies of patients, with potential applications ranging from research to diagnostics.

Color me surprised

X-ray imaging works by pushing high-energy radiation through your body onto a recording plate (or ‘film’). The denser bits inside you, most notably bone, block or absorb these rays. Your more fleshy bits — such as muscle, organs, and other soft tissues — generally allow X-rays to pass straight through. Radiation enters a particular area, exits the body, and reacts with the recording plate. Soft tissue, which lets a lot of this radiation pass, will appear dark on the recording. Areas that allowed relatively little radiation to pass through will show up as white.

It’s a really nifty way of looking inside the body. It only produces black and white images, and often with blurry contours — but it’s typically accurate enough for what we need it to do. A doctor can still tell if one of your bones is broken by looking at an X-ray. It doesn’t matter very much if the image only shows two colors without crisp lines, as bones tend to be quite obvious.

With the new technology, the ‘X-ray’ part of the new device works largely the same way. The real advance is what it does with the readings.

Ankle x-ray color.

A human ankle as seen through the new X-ray device.
Image credits: MARS Bioimaging.


Strictly speaking, the scanner itself doesn’t produce the colors — they’re generated after the readings are completed. The device draws on a combination of Medipix technology. “Medipix is a family of read-out chips for particle imaging and detection,” Cristina Agrigoroae wrote for CERN (the European Organization for Nuclear Research). It works like a camera, detecting and counting each individual particle hitting the pixels when its electronic shutter is open.

Medipix was first developed to help CERN researchers track particles in the Large Hadron Collider — and computer algorithms to ‘gauge’ the color of your tissues.

Essentially, it all boils down to how the device records radiation after it passes through a patient’s body. Traditional X-ray devices record whether these waves pass through bone or soft tissue; meanwhile, MARS Bioimaging’s device records the intensity of the outcoming radiation. Based on these values, which are contingent on the make-up of the tissues they pass through, the algorithm fills in colors to represent your bones, muscles, and other tissues.


Timepix3, one of the read-out chips of Medipix.
Image credits CERN.

But, if traditional X-rays are just good enough to spot broken bones, why do we even need all these colors? Won’t just they confuse our doctors? Well, not really.

The main benefits of the new technology are much better resolution (crisp images) and the ability to spot issues with both the bones and their surrounding tissues.

“This technology sets the machine apart diagnostically because its small pixels and accurate energy resolution mean that this new imaging tool is able to get images that no other imaging tool can achieve,” says Phil Butler — a physics professr, co-founder of MARS Bioimaging, and one of the researchers behind the device — in a CERN news release.

For example, Phil and his partner Anthony Butler (Phil’s son and a bioengineering professor) have already made the device available for a number of studies in areas that typically had little use for X-ray scanners — such as cancer or stroke research.

“In all of these studies, promising early results suggest that when spectral imaging is routinely used in clinics it will enable more accurate diagnosis and personalization of treatment,” Anthony Butler explains.

The duo plans to test their scanner in a New Zealand trial focused on orthopedic and rheumatology patients. However, they caution that even if the trial goes swimmingly, it might still take years for the technology to get all the regulatory approval it requires before it can be used on a wide scale.

Researchers find oldest pigmented biological molecules — they’re bright pink

You probably wouldn’t have much to see if you’d go back in time 1.1 billion years. Multicellular life was just starting to develop, and plants were yet to develop. But life, in its primitive, early stages, was already very active. For instance, a group of sea organisms was busy producing chlorophyll — and researchers have now found fossilized molecules of these organisms, which they believe to be the oldest colored molecules we’ve ever found.

Biogeochemistry lab manager Janet Hope holds a vial of colored porphyrins (pink colored liquid), which researchers believe to be some of the oldest pigments in the world. Photograph: Lannon Harley/Australian National University.

Naturally, most things are colored, but it took a while for life to be able to develop its own hues.

“Of course you might say that everything has some colour,” said the senior lead researcher, Associate Prof Jochen Brocks from the Australian National University (ANU). “What we’ve found is the oldest biological colour.”

It all started with researchers grinding samples of shale rock. ANU Ph.D. student, Dr. Nur Gueneli, was running an organic solvent through the powdered rock, a process similar to what you’d see in a coffee machine. Gueneli was thrilled when she realized what she had stumbled upon.

“I heard her screaming in the lab when it came out, and she ran into my office,” Asst Prof Brocks told the BBC. “At first I thought it had been contaminated. It is just amazing that something with a biological colour can survive for such a long time.”

Subsequent analysis revealed that the pigment was produced by cyanobacteria.

This doesn’t mean that we know what color the cyanobacteria had when they were living, however. For instance, a dinosaur bone would have its own color, but that doesn’t tell you anything about the color of its skin.

The finding doesn’t only go skin deep. While it’s always exciting to discover something colored and cool, the discovery will also help solve an important puzzle about life: why large, complex creatures took so long to develop.

The Earth as a planet is about 4.6 billion years old, but more complex creatures like seaweed only emerged some 600 million years ago. Brocks says that the cyanobacteria producing these pigments were very small — even 1,000 times smaller than microscopic algae alive today. So for animals existing at the time, the cyanobacteria didn’t provide much of a meal — which means no stable food chain. In other words, you can only get big if there are big enough things to eat around you.

The study has been published in journal Proceedings of the National Academy of Science of the United States of America.

Ecological restoration of moths in the Cretaceous Burmese amber forest. Credit: YANG Dinghua.

Scientists uncover secret color of 200-million-year-old butterfly wings

Ecological restoration of moths in the Cretaceous Burmese amber forest. Credit: YANG Dinghua.

Ecological restoration of moths in the Cretaceous Burmese amber forest. Credit: YANG Dinghua.

Butterflies have fascinated humankind for millennia and have been interpreted in a variety of ways, from omens of love to personifications of the soul. Part of their appeal lies in their wings’ iridescence, where the same principle behind soap bubbles applies — only at a whole new level.

As small as they are, butterfly wings are covered by thousands of microscopic scales, split into two to three layers. Each scale is comprised of multiple layers separated by air. So, what happens is the many equally-spaced layers of the butterfly wing create multiple instances of constructive interference, rather just a single instance from the top to the bottom as is the case in a soap bubble. In some species, such as the morpho butterfly, the resulting effect can be astonishing.

But, unlike pigments, which can survive for millions of years, structural colors are far more difficult to interpret from fossils. Luckily, Chinese researchers at the Nanjing Institute of Geology and Palaeontology, in collaboration with colleagues from Germany and the UK, were able to use novel methods to find that butterflies have been sporting this sort of flashy display for a long, long time.

Wings and scales of Jurassic Lepidoptera and extant Micropterigidae. Credit: ZHANG Qingqing et al.

Wings and scales of Jurassic Lepidoptera and extant Micropterigidae. Credit: ZHANG Qingqing et al.

The team used a combination of advanced imaging techniques on more than 500 ancient butterfly specimens to reveal the wings’ ultrastructures — the architecture of cells visible with magnification. Only six specimens were well preserved enough to be of use, including a 200-million-year-old insect. Most of the butterflies were fossilized in stone, which means their pigment color is gone, but their nanostructure lingered.

By examining the fossilized under an electron microscope, the researchers were able to discern the wings’ pattern: an upper layer of large fused cover scales and a lower layer of small fused ground scales, plus preserved herringbone ornamentation on the cover scale surface. Optical modeling allowed the researchers to infer the structural patterns and characterize the wings’ optical properties.

Tarachoptera from mid-Cretaceous Burmese amber. Credit: ZHANG Qingqing et al.

Tarachoptera from mid-Cretaceous Burmese amber. Credit: ZHANG Qingqing et al.

This analysis suggests that the ancient insect had a color pattern nearly identical to those found on several extant species from the Micropterigidae superfamily — the most primitive extant lineage of Lepidoptera, the insect order that includes butterflies and moths. Optical modeling confirmed that diffraction-related scattering mechanisms of the fossil cover scales would have displayed broadband metallic hues as in numerous extant Micropterigidae, as reported in the journal Science Advances.

Judging from these findings, it seems like the iridescent pattern of wing scales have been an integral part of the Lepidoptera family at least since the Jurassic. Future studies will characterize the optical response of scale nanostructures in other fossil specimens in order to determine the models of the evolution of structural colors in Lepidopterans.

Sei Arabella coloration.

World’s first blue chrysanthemums are lab-engineered but look really pretty

Naturally blue chrysanthemums are now reality — and it’s all because biochemists at the National Agriculture and Food Research Organization in Tsukuba, Japan toyed around with the flower’s genome.

Sei Arabella coloration.

Image modified after N. Noda et al., 2017.

Blue flowers aren’t that common in nature. Off the top of my head I could recall… morning glory? Maybe forget-me-not’s? Those might be blue. For some reason, it’s just not very popular a color with good old mother nature. And statistically unsurprising, there are many more species that definitely aren’t naturally blue; among then, the chrysanthemum, which flower in shades of pink and red.

However, that’s about to change. Naonobu Noda, a plant biologist at the National Agriculture and Food Research Organization in Tsukuba, Japan, has coaxed a strain of chrysanthemum to turn blue by adding two genes to the plant’s genome.


According to a color scale put together by the Royal Horticultural Society, most flowers you think are blue are actually shades of violet or purple. Florists and breeders are keen to get their hands on new colors and varieties of plants, and blue is especially sought-after because of its rarity.

However, turning flowers blue (naturally blue, not by dying them) has proven ridiculously difficult up to now. ‘True’ blues, as described by the Royal Horticultural Society’s chart, requires a complex interplay of chemical compounds. The molecules that lend petals, stem, and fruit their colors are known as anthocyanins. These mostly consist of aromatic ring compounds that can shine red, purple, or blue depending on what extra compounds — like sugars or groups of atoms — are tied to them.

Intra-cell conditions, like wall thickness, size, or shape, also factor in, however: so simply taking the anthocyanins from a blue flower and grafting them into a new one won’t turn it blue.

Noda overcame these issues by genetically tailoring reddish chrysanthemums to be blue. First, he grafted a gene from a bluish flower called the Canterbury bell into a chrysanthemum to make it take a purple hue instead. Then, Noda and his colleagues mixed in a second gene, this one taken from the blue-flowering butterfly pea. This would dictate the addition of a sugar to the plant’s anthocyanin, taking the flower from purple to full on blue. The team believed a third gene would be required to reach this step, but chemical analyses later revealed that chrysanthemums naturally produce a colorless component that reacted with the modified anthocyanin to create blue.

Next, Noda’s team aim on creating blue chrysanthemums that can’t reproduce, so they can be safely commercialized. How commercially successful the flowers turn out to be is still anyone’s bet, given that GMOs are still a hotly debated topic. Perhaps the blue chrysanthemums will finally help swing the public vote — one way or another.

The paper “Generation of blue chrysanthemums by anthocyanin B-ring hydroxylation and glucosylation and its coloration mechanism” has been published in the journal Science Advances.


Why eyes have different colors: a science-based look


Credit: LittleThings.

It is said that the eyes are the doorway to the heart; a reflection of our inner self and emotions with countless poets, writers, and artists praising this unique quality. Whether or not this is the case, eyes are deeply fascinating and have been so since time immemorial. But for all this, they’d certainly be far less interesting, and perhaps even frightening, if they weren’t colored.

Actually, all the magic happens within the colored part of the eye: the iris.

What gives eyes their color

The iris color is determined by the amount of melanin pigmentation. The more pigment there is, the darker the iris will be. Blue, gray, and green eyes are lighter because there is less melanin inside the iris.

By far, the most common eye color in the world is brown, with over 55% of the population falling into this category. Depending on where a person is born, eye color demographics can vary wildly. For instance, nearly all persons of African and Asian ancestry have brown eyes. It’s believed up to 10,000 years ago, all humans had brown eyes only. Then a mutation turned off the pigmentation on the front of the iris.

Hazel eyes are similar to brown eyes, the distinction being these are lighter. A defining trait of hazel eyes is their multi-coloured appearance that can vary from copper to green depending on the lighting. Hazel eyes have a higher concentration of melanin around the iris’ border. Estimates suggest 5 to 8 percent of the world’s population is hazle-eyed (both green and brown).

The next most common eye colors are blue, gray, and green in this order. It’s commonly quoted that only 2% of the world’s population has green eyes.

There are also so-called ‘amber’ eyes. which are even rarer than green eyes. Amber eyes or ‘wolf eyes’ as they’re sometimes called are completely solid and have a strong yellowish, golden, or russet and coppery tint. They can also contain a small amount of gold-ish gray. It’s not clear how amber eyes form but some suggest it’s due to the increased presence of a pigment called lipochrome (also known as pheomelanin).

Lastly, people with albinism, a condition that causes a complete lack of or very low levels of pigment in the skin, hair, and eyes, sometimes appear to have violet or red eyes. Because albino people essentially lack pigment in the iris, light simply bounces off the back of the eye. Albino eyes may appear red because the light reflected first off blood vessels at the back of the retina. This is the same reason why you sometimes appear red-eyed in photos. The eyes can appear violet in certain lighting conditions when the red color mixes with the bluish color resulting from light-scattering effects — basically for the same reason why the sky is blue.

The table below shows how melanin content influences eye color.

[panel style=”panel-info” title=”Iris pigmentation and coloring” footer=””]


Eye color

Melanin Presence (front layer)

Melanin Presence (back layer) 

Dominant Pigment Type










Even less than blue




More than blue eyes, less than brown




More than green, less than brown


Pheomelanin and Eumelanin





Red or Violet

None or extremely little

None or extremely little




Besides making eyes colored, the pigment melanin also serves the vital function of protecting them from the sun’s UV rays. It follows that darker eyes, which have the most melanin, are less sensitive to the sun’s harmful rays than lighter eyes like blue.

When we come into this world, our eyes are blue or almost colorless. This is true for all babies, no matter their ancestry. In time, the concentration of melanin increases and by age three, the eyes will have darkened to their true, final resting color. Or almost final. Much later in life, our eyes can change color once more. Disease and trauma can also inflict changes in iris coloring. More on that later.

How eye color is inherited

Note that this chart only takes into account parents’ eye colors. Because it only factors in the phenotype (i.e. what color the eyes appear) and not the genes themselves, it is not going to be 100% accurate in every case. Credit: SittingAround.

Note that this chart only takes into account parents’ eye colors. Because it only factors in the phenotype (i.e. what color the eyes appear) and not the genes themselves, it is not going to be 100% accurate in every case. Credit: SittingAround.

If both parents have blue eyes, there’s a good chance their offspring has blue eyes as well. It follows that iris coloring is governed by genetics. However, a baby’s eye color doesn’t come out as a blend of the parent’s eye, as if you mixed paint. Up until not too long ago, even doctors used to think used to think that eye color was determined by a single gene and followed a simple inheritance pattern in which brown eyes were dominant to blue eyes. The thinking was that if two parents both had blue eyes, they couldn’t make a baby with brown eyes. Imagine what sort of problems this caused back at home. Alas, this is wrong.

Instead, many various possibilities exist since each parent has two pairs of genes on each chromosome. In other words, eye color is a polygenic trait, meaning it is determined by multiple genes.

The eye color genes

Among the genes that affect eye color, OCA2 and HERC2 stand out. Both of these genes are found in the human chromosome 15. The OCA2 gene produces a cell membrane transporter of tyrosine, a precursor of melanin. Mutations in OCA2 result in oculocutaneous albinism, a condition associated with vision problems such as reduced sharpness and increased sensitivity to light. HERC2 regulates the OCA2 genes’ expression. In the European population, a common polymorphism in HERC2 gene is responsible for the blue eye phenotype. A person who has two copies of C allele at HERC2 rs1293832 will likely have blue eyes while homozygous TT predicts likely brown eyes.

[panel style=”panel-success” title=”Eye color inheritance ” footer=””]

Likelihood of eye color for people of European descent 85% chance of brown eyes;
14% chance of green eyes;
1% chance of blue eyes.
72% chance of blue eyes;
27% chance of green eyes;
1% chance of brown eyes.
56% chance of brown eyes;
37% chance of green eyes;
7% chance of blue eyes.



Several other genes play smaller roles in determining eye color. Some of these genes are also involved in skin and hair coloring. Genes with reported roles in eye color include ASIP, IRF4, SLC24A4, SLC24A5, SLC45A2, TPCN2, TYR, and TYRP1. The effects of these genes likely combine with those of OCA2 and HERC2 to produce a continuum of eye colors in different people.

Nowadays, many DNA tests are reliable enough to determine a person’s eye color from a hair sample alone, some with over 90% accuracy. Such analyses are now becoming more and more common in the field of forensic investigations.

How eye color changes during lifetime

The iris, the colored bit of the eyes, is essentially a muscle. Its role is to control pupil size so we can see better under varying lighting conditions. When there’s dim light, the pupils enlarges and, conversely, grows smaller in bright lighting. Pupils also change size depending on focused objects. For instance, reading a book requires your pupils to shrink in order to focus on the near objects, i.e. words inked on the paper.

When the pupil’s size changes, the melanin pigment is compressed or spread apart, slightly changing the eye color. The effect is minuscule but it’s there.

The iris is a muscle that expands and contracts to control pupil size. The pupil enlarges in dimmer lighting and grows smaller in brighter lighting. The pupil also shrinks when you focus on near objects, such as a book you are reading.

When the pupil size changes, the pigments in the iris can become compressed or spread apart, changing the eye color a bit. Some have suggested that mood can also change eye color. While it’s true certain emotions like anger or love can influence pupil size, the iris doesn’t really change color. When a  person’s eyes have red, dilated blood vessels from anger, his eyes may appear to be greener because of the contrast, that’s all.

Eye color can permanently change over the course of one’s life, though. For 10 to 15 percent of the Caucasian population, iris color changes with age. For instance, hazel eyes can get dark with age. And if such a change in eye color happens fast and dramatically, like from brown to green or from blue to brown, this may be a sign of concern making a doctor’s appointment urgently required.  Eye color changes can be a warning sign of certain diseases, such as Fuch’s heterochromic iridocyclitis, Horner’s syndrome or pigmentary glaucoma.

The eye color infographic

How butterflies have such a beautiful colour

Butterflies are some of the most exquisitely patterned and coloured creatures in the world. The colours all start with the scales on their wings. The scales contain crystals called gyroids that are made of chitin, the substance that is also in insect exoskeletons. These structures are complex and just a few nanometers large — so extremely tiny. Nanotechnology, creating tiny structures for industry, also creates such small-scale structures. They are important in areas such as medicine, electronics, and space travel. However, the nanostructures on butterfly wings are way more complex than anything that can be man-made. A group of researchers examined how the crystals develop on a butterfly’s wing for potential uses in industry.

The small Hairstreak. Image credits: Wilts et al., 2017.

The study that is published in Science Advances set out to discover how these crystals that give butterflies their magnificent colour form. It isn’t yet possible to study a butterfly’s wing while it’s developing, so the researchers examined the scales of a grown butterfly under extreme magnification. The subject? The small Hairstreak butterfly Thecla opisena from Mexico. The upper side is jet-black with blue patches while the lower side is green with a small red patch on the bottom edge of the wing. However, if you zoom into the bright green wing it’s actually not all green. The cover scales are bright green while the background is an orange-red colour. The cover scales themselves are not completely green but are made up of several domains that don’t overlap.

A close-up of one wing scale wing; it has a red background with green domains on top. Image credits: Wilts et al., 2017.

Each scale contains structured nanocrystals that interestingly, were spatially separated and loosely connected to the lower surface of the wing. On the wing, the crystals were arranged in lines, and at the beginning of the line the crystals were really small but as you progress further down the line, the crystals get larger. Perhaps, the scales form this way and are constantly growing on the wing. They seem to be developmental stages frozen in time and show the process of how these crystal form. The way that the scales develop is likely that the casing forms first and then the internal gyroid structure follows.

How the crystals develop over time. Image credits: Wilts et al., 2017.

We do need to keep in mind that this is just one butterfly out of more than 140,000 species. However, it is likely, according to the authors, that this way of development can be generalised to most wing scales and that all butterflies get their colour in a similar way. They could be very useful for nanotechnological applications, such as light-guiding technology because they can manipulate light in arbitrary directions. It is interesting to see how the natural world inspires technological advances.

Journal reference: Wilts, B.D. et al., 2017. Butterfly gyroid nanostructures as a time-frozen glimpse of intracellular membrane development, Science Advances.

Color Dots.

Biology imparts us with instinctive color categories — culture only shapes them

Although different cultures go about ordering colors into different systems, all babies seem to share a set of common, instinctive color categories.

Researchers have a pretty good grasp of how humans see colors. Different wavelengths of light reflected by various objects go through the pupil and lands on the retina, where specialized cells (known as cones) pick up on either short, medium, or long wavelengths. They send this information up to the brain where it all gets put together and processed into the final image we see.

Color Dots.

But although every human out there sees the same way, we have different systems for explaining what we see. Some languages, like Japanese, don’t necessarily make the distinction between green and blue, two colors which most of you reading this take as obviously distinct. Culture has a big part to play in shaping how we group colors, but previous research has also shown that babies also have a kind of built-in color category system.

So how do these two fit together?

To find out, a team from the University of Sussex has studied the responses of 176 babies aged between four to six months to patches of color. They report that while cultural context does play a part, our brains are naturally inclined to bunch colors up into five basic categories.


The infants were seated in front of a wooden booth which had two windows cut out at the sides. Initially, both windows repeatedly showed the same color, but as the experiment progressed, one of them was filled with a different color at random. This new pairing was then shown multiple times, and the babies were recorded with a webcam to capture their reaction. Each baby was shown only one pair of different colors, with at least 10 babies tested for each pair.

“We wanted to find out what’s the connection between two [color categories and groupings], what is it that babies are using to make their colour categories and what can that tell us about the way we talk about colour as adults,” said said Alice Skelton, first author of the research and a doctoral candidate at the University of Sussex.

The team was looking for a phenomenon known as novelty preference in the babies — the infants will look at the second color for more if they perceive it to be different from the first-shown color. So if babies consistently look more time at the new color, even if they’re really close together on the color spectrum, that would suggest that our brains perceive it as belonging to a different category.

Some of the infants were shown very similar pairs of colors, while others were shown pairings farther apart on the color spectrum, to get a feel for where their boundaries of color categories fell. Fourteen different colors throughout the color spectrum and of the same lightness were used in total. The results show that babies order colors under five basic categories: red, yellow, green, blue, and purple.

The next step was to compare these categories to color groupings in English and 110 other nonindustrialized languages. There were obviously several differences in the way different cultures went about ordering color (such as different numbers of categories, their placement on the spectrum, and exact boundaries) but overall, their systems tied well with the five categories the team found.

Build-in color

“Infants’ categorical distinctions aligned with common distinctions in color lexicons and are organized around hues that are commonly central to lexical categories across languages,” the authors write.

“The boundaries between infants’ categorical distinctions also aligned, relative to the adaptation point, with the cardinal axes that describe the early stages of color representation in retinogeniculate pathways, indicating that infant color categorization may be partly organized by biological mechanisms of color vision.”

What’s more, four of the color boundaries the infants exhibited mapped the four extremes signals from the cone cells can produce when they are processed and interpreted in the brain. Taken together, these findings suggest that biology creates our color categories, and environmental as well as cultural factors shape them afterward — if your language doesn’t differentiate between green and blue, for example, babies learn not to make that distinction either as they age.

The findings are important as they lend a lot of weight to the color universality theory since infants show a definite color categorical structure long before they learn the words for them.

But the paper isn’t without its limitations. First off, there is a possibility that the colors the babies were exposed to from birth, for example in toys or wallpaper colors, could have determined their brain to create certain color categories. Since the study included only children from the UK, they were likely to have lived in similar conditions and be exposed to roughly the same color schemes. Retaking the test with children from other cultures should show whether these five categories are learned or instinctual.

The team now hopes to explore how our categories shift as we develop language.

The paper “Biological origins of color categorization” has been published in the journal Proceedings of the National Academy of Sciences.

Nightjar bird.

A more limited range of color vision might help predators see through camouflage, research finds

Most animals can perceive fewer colors than humans can — while others can see many more. Scientists at the University of Exter have looked at the comparative advantages of di- and trichromatism in finding camouflaged birds in pictures to understand why so many species rely on this limited range of color vision.

Basic colors.

Sometimes less is more — but that doesn’t really stand for color receptor cells. Humans have three kinds of these cells on our retinas, so our vision revolves around three basic colors, making us trichromats. But a large number of other animals, including the majority of mammals today, are dichromats who only have two kinds of color receptor and see everything as a mix of only two colors. On the other hand, many bird species (and this one lady) are tetrachromats, and some invertebrates can pick up on many more colors.

But back to dichromats. Most of them are red-green color blind, and that’s also the most common type of color blindness in humans. Moreover, some primate species show color vision polymorphism, meaning certain females are trichromats but most individuals are dichromats. Add all this evidence together, and it begs the question — is there an evolutionary advantage for seeing only two colors instead of three? To find out, a team from the University of Exter has created an online computer game and unleashed it upon the web, where more than 30,000 people played it.

The concept was pretty simple: players were shown photographs either in normal color or in simulated dichromatic vision. There were camouflaged nightjar birds or their nests, containing eggs, somewhere in the image — and the players had to find them.

Nightjar bird.

Example of a nightjar seen in trichromat (left) and dichromat (right) vision.
Image credits University of Exeter.

Seeing a more limited range of colors should make dichromat predators more adept at finding prey since there’s less color, so to speak, to help hide a well-camouflaged dinner. Dichromats should thus have an easier time differentiating between light and dark areas and finding hidden objects, for example — an advantage any aspiring predator would want.

But the team was surprised to find that participants looking at trichromat photos were actually faster at finding the nightjars and eggs that their counterparts. There were large variations in the performance of dichromat players from photo to photo — depending on factors such as camouflage patterns or brightness. Furthermore, over the course of the game, dichromats improved their game faster than trichromats, and by the end of the game, both groups performed equally well.

So it is possible that their performance was worsened as their brains learned the ins and outs of dichromatic vision. It may be that, given a longer period of time to adjust, they could become even better than trichromats at spotting the eggs.

” These results suggest there are substantial differences in the cues available under viewing conditions that simulate different receptor types, and that these interact with the scene in complex ways to affect camouflage breaking,” the team concludes.


The paper “Relative advantages of dichromatic and trichromatic colour vision in camouflage breaking,” has been published in the journal Behavioural Ecology.

Scientists find a woman that can see 99 million more colors than you or me

Neuroscientists in the UK have recently announced that their 25 year long search for a tetracromath — a person with an extra type of cone cell in his or her retina — has finally come to a successful end. They estimate that the woman can see a staggering 99 million more colors than other humans, and they believe there are many more people like her waiting to be discovered.

Image via pixabay

Our eyes‘ retina house cone cells that can distinguish color variation in incoming light. Humans usually have three types of cone cells, each able to detect the presence of a single color — green, red, or blue — and are thus known as “trichromats.” Most color blind people and most other mammals only have two different types of cone cells, and are “bichromats.” As each cell can distinguish between 100 or so shades of the same color, each extra type of cone cell increases the number of colors we can see exponentially. So where a color blind person can see around 10,000 shades, a healthy human can see around 1 million different colors.

But what if human beings had not three, but four types of cone cells in their retinas? That would allow a person to see 100 million colors — colors most of us have never even dreamed of, colors we have no way of even imagining. The existence of such people, or “tetrachromats,” was first proposed in 1948 by Henri Lucien de Vries, a Dutch scientist researching with color blind patients. He found that while his male subjects had two types of normal cone cells and one mutant type that was less sensitive and didn’t pick up on its corresponding color (either green or red,) the female subjects had three normal cone cell types and one mutant type. Even if this extra type of cell didn’t actually do anything, it suggested that humans can have more than three types of cells.

Interest in tetrachromats largely died out until the late ’80s, when Professor John Mollon from Cambridge University started looking for women who might have four functioning cone cell types. He estimated that, if color blind men could pass this fourth cell type to their daughters, around 12% of the female population should be tetrachomats. However, he never actually found a person with four different fully functional types of cone cells, a tetrachromat.

But now, 25 years after they’ve first started searching, UK scientists believe they’ve finally found such a woman. Known as cDa29, she was identified by Newscastle University neuroscientist Gabriele Jordan, a former coleague of Mollon, after she decided to use a different test than those the professor employed in his search.

She took 25 women who had a fourth type of cone cell, and put them in a dark room. Looking into a light device, three colored circles of light flashed before these women’s eyes. To you and me the circles would look the same, but Jordan believed that a true tetrachromat could tell them apart, as the fourth type of cone cells would allow her to pick up on the subtle differences.

One of the women tested, cDa29, was able to differentiate the three different colored circles on every single try.

“I was jumping up and down,” Jordan told Discover magazine.

But why did it take so long to find a tetracromat if there’s so many of them? One issue is that the team only carried out their search in the UK. But more importantly, Jordan says, is that most true tetrachromats simply don’t know they’re any different from the rest of us.

“We now know tetrachromacy exists,” she said. “But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.”

Jay Neitz, a vision researcher at the University of Washington, who wasn’t involved in the study, thinks that tetrachromats simply haven’t had a chance to use their eyes to their full potential in our society.

“Most of the things that we see as coloured are manufactured by people who are trying to make colours that work for trichromats,” he said. “It could be that our whole world is tuned to the world of the trichromat.”

The research on cDa29 hasn’t been peer-reviewed or published as yet, and Jordan is continuing her research and search for more tetrachromats. Her results still need to be verified but if tetrachromats really do exist, it could teach us a lot about how vision works.

One thing we might never be able to understand, however, is exactly what the world looks like through cDa29’s eyes.

“This private perception is what everybody is curious about,” Jordan told Discover. “I would love to see that.”