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How a dog sees a rainbow, and 12 other images that explain how we see color

Randall Munroe,

The Internet furor over “the dress” has mostly subsided, but its status as the ultimate symbol of media frivolity is likely to last. But there was also something deep about the dress, both scientifically and philosophically. For many, it was unsettling to discover that something they saw as literally black or white was, to someone else, blue or gold.

The dress, which “totally derailed” the annual meeting of the Macula Society in Scottsdale, Ariz., hinted at a more profound questions about how our perceptions of the world differ. Is what I see as “blue” really the same thing as what you see as “blue”? Or have we both learned the same name for something that looks different to each of us?

As is turns out, no one really has an answer to this question. The colors that people see are shaped by physiology, for example colorblindness, and by language. Cultures that have no word for blue have a much harder time spotting it.

Consider a rainbow. We see the standard "ROYGBIV" (red, orange, yellow...) spectrum. But a dog sees a less vivid image, while a butterfly can see many more colors than a human.

We can't show you a visualization of what a rainbow looks like to a butterfly. But WNYC Radiolab did a cool representation with sound, in which they had a choir sing a note for each color an animal can see. For the dog's rainbow, the choir sang only two notes. For humans, they sang seven, and for the butterfly, a much fuller, more complex chord.

What's going on here? To understand color, you need a (brief!) dose of basic science. Colors are just different wavelengths of visible light, and the color of an object depends on what kinds of light it absorbs and which it reflects. Different elements and compounds absorb different wavelengths of light, and color results from the light that bounces back and hits the eye.

A green leaf, for example, reflects green wavelengths of light and absorbs everything else. When leaves change color in the fall, it’s because their chemical composition, and thus the kind of light they absorb and reflect, is changing. As temperatures cool and sunlight fades, the chlorophyll that gives leaves their green color begins to break down, allowing colors from longer-lasting compounds that reflect yellow, orange and red to come to the fore.

It’s not until these wavelengths hit our brains that they become what we think of as color. Color is basically a product of the brain.

Humans have three different types of cone cells, which are responsible for color vision, in their eyes. We have receptors for the wavelengths that create red, green and blue – which enable us to see all combinations of those colors. Dogs only have two cones, for blue and yellow -- which is why the dog's rainbow above looks quite a bit duller than ours. Many animals can see more colors than humans and dogs: Butterflies may have up to five cone receptors, while the humble mantis shrimp has 12.

Some humans have only two working receptors; they are the people we commonly term as “colorblind.” It turns that what they see is somewhat similar to the average Labrador.

The two most common types of color blindness, deuteranopia and protanopia, affect the green and red cone cells, respectively. Both conditions make it difficult to distinguish between red and green (and follow traffic rules, as the image below by Martin Krzywinski, a staff scientist at the Michael Smith Genome Sciences Centre, shows). Tritanopia, blue-yellow colorblindness, is more rare.

Colorblindness is actually fairly common. Among men, about 8 percent of Caucasians, 5 percent of Asians and 4 percent of Africans are red-green colorblind. Colorblind people can recognize a wide range of colors, but certain ranges of colors are hard to distinguish. Those who are red-green colorblind have trouble distinguishing between colors that differ only in their red or green component. The chart and Spock tribute below show some of these colors.

Colorblindness mostly affects men, since the genes encoding red and green receptors are located on the X-chromosome, of which men only have one. Women have two, meaning they have a greater chance of getting a normal gene to balance out a defective one.

Because they have two X chromosomes, women also theoretically have the potential of being “tetrachromats” – people with four types of color receptor cells instead of three. Though the evidence remains inconclusive, some researchers believe this fourth receptor allows tetrachromats to see a much wider range of colors.

A visualization by Stephen Von Worley, built on a color survey with more than 5 million results, suggests that women certainly identify more colors than men do. The circles are positioned horizontally by hue and vertically by gender preference, with women using the color names toward the top and men using those toward the bottom. The size of the circle indicates how often the color name was mentioned.

Right away, the proliferation of small dots above the line suggests that women typically give a wider variety of names to colors than men do. But this doesn't prove that women can "see" more colors than men. The difference could be due not to genetics but to the kind of product marketing that targets women: Some of the color names that women suggested sound like they could be used to sell sweaters or eye shadow – like “dusty teal” and “pale sage.”

In fact, most women with four color receptors seem unable to distinguish the slight variations in color that a tetrachromat should be able to see. Gabriele Jordan, a Newcastle University neuroscientist who studies tetrochromacy, estimates that as many as 12 percent of women have four cones, but the vast majority of her test subjects saw nothing beyond the ordinary.

Even if some women can detect a broader range of colors, they may never realize or develop their ability to do so. After all, the manufactured goods that surround us are designed by and for standard, three-coned humans, including the images spit out by our TVs and color printers. Unless someone is a painter or a florist, they may not have much exposure to colors that a trichromat can't see.

Here's where things get really crazy: Beyond mere exposure, part of the reason that people with four cones can't see other colors is likely linguistic and cultural. The colors we collectively recognize and give names to are derived from the color wheel. Even if a tetrochromat encountered a new color, they wouldn’t know what to call it, or how to talk about it with other people. And that might, in a certain sense, limit their ability to “see” it.

Many anthropologists, linguists, psychologists, philosophers and educators have argued that language shapes our perception of reality. As linguist Guy Deutscher wrote for The New York Times, it's not that language forbids us from seeing anything, but that having words for certain things obliges us to look at them more intently.

The way different cultures categorize color varies a lot. As WYNC’s Radiolab points out in a fascinating episode about color, historical documents show that civilizations acquired words for different colors over a very long expanse of time – and usually in roughly the same order. Most human societies appear to have acquired the names for black and white first, followed by red, then other colors of the rainbow, and, only very lately, blue. The Homeric epics, old Icelandic sagas, ancient Chinese stories, Vedic hymns and the Bible all lack specific references to “blue,” despite numerous descriptions of the sky and sea.

Radiolab suggests this sequence for acquiring colors might have something to do with the human ability to manufacture them. Red, the first color to pop up in most ancient languages, is one of the easiest colors to produce anywhere in the world, since it can be made of clay. Blue pigments are much rarer in nature.

The Chinese still retain a mysterious color word in their language, "qing," that is evidence of a time before blue and green were separate categories. Today Chinese has a separate word for blue, but the character "qing," which often refers to plant life, can still refer to a range of natural colors.

It seems strange to us, but many cultures don't distinguish between green and blue. That includes the Himba of northern Namibia, a group who were the subject of a color study by Debi Roberson and Rick Hanley of the University of Essex. English has about 11 color categories, but the Himba have only six, and their divisions are much different than our own. The chart below demonstrates how the Himba categorize colors. “Burou” is the label for what many Westerners see as a diverse group of blues and greens. 

Image courtesy of Debi Roberson and Richard Hanley, and illustrated by Carolyn Arcabascio. Image originally published in the GLIMPSE journal blog and in GLIMPSE journal issue #4, Color.'

Roberson’s study suggests that these different descriptions affect the way the Himba see colors. For example, the Himba have different words for shades that we would both classify as green. Because of this, they had little difficulty finding the one green square below that is a slightly different shade from the others. Can you see it? Take a guess before you scroll down.

Here it is:

Amazingly, the Himba test subjects had a much easier time with the test above than the one below. Their language doesn’t distinguish between blue and green, making the blue square below (which practically leaps out from the screen for English-speakers) much harder for them to spot. If that still seems crazy, you can watch them perform the experiment in this video.

We take it for granted that the sky and the sea are blue. But what we see as "blue" is clearly not the same for the Himba, who describe the sky as black and water as white. Whether it's due to physiology, culture, or language, it turns out that color is a much trickier concept than a basic pack of Crayons suggests.