A small group of people can see «invisible» colors that no one else can, discovers David Robson, a columnist for BBC Future. How do they do that?
When Concetta Antico took her students to the park for an art lesson, she would often ask them about the different shades that she could distinguish.
«I’d say, ‘Look at the light in the water: can you see the pink shining through the rock? Can you see the red on the edge of that sheet?'» They nodded their heads.
Years later, she realized that it was only out of courtesy that they did not tell her the truth: the colors she saw so vividly were invisible to them.
Today, she knows that this is a symptom of a condition known as «tetrachromatism.»
see the unseen
People like Antico can see colors that are invisible to most of us.
Think of a gravel driveway. What we see in a sober gray color shines like the window of a jewelry store for Antico.
«To me, the little stones pop orange, yellow, green, blue, and pink,» she says. «I was very surprised when I realized what others are not able to see.»
Tetrachromats are quite rare, and because he is an artist, Antico is able to give us a glimpse into his world.
According to Kimberly Jameson of the University of California, Irvine, who has studied Antico extensively, its case may even suggest ways for more people to see the same thing.
Are we going to the same?
The question of whether we all see the same colors has been widely questioned throughout the history of philosophy and science.
Almost everyone has three types of cones, the light-sensitive cells located in the retina, each responding to light of a different bandwidth.
The color of an object depends on the particular combination of these signals and, although the sensitivity can vary between people, in general the colors that one person sees match those of another.
Color blind people would be the exception, since one of their cones is defective. Their reduced sensitivity to certain wavelengths makes it difficult for them to distinguish between reds and greens, for example.
The X factor of the cone
Thanks to a mutation in a gene that influences retinal development, tetrachromats have an extra cone, and by some estimates their existence offers as many as a hundred different variants for every color normally perceived by humans.
We know this happens in nature: Zebra finches and goldfish have a fourth cone that would seem to help differentiate apparently identical colors.
Proving that it occurs in humans was more difficult.
Some 20 years ago, Gabriele Jordan of the University of Newcastle and John Mollon of the University of Cambridge argued that it might be possible in humans.
The crux of the argument was the fact that the genes for our red and green cone types are located on the X chromosome.
Since females have two X chromosomes, they may have two different versions of the genes, coding for sensitive cones at slightly different ranges of the spectrum. In addition to the other two unaffected cones, they would have four in total, that is, they could be tetrachromats.
For that reason, it’s thought to be a condition unique to women, although researchers can’t totally rule out the possibility that men also inherit it in some way.
That was the theory, but it shows that there are women who see the world in a different way, it has involved two decades of work.
Although the corresponding combination of genes does not appear to be particularly rare (it is possible that 12% of women have four different cones), many showed no perceptual differences.
But around the year 2010, the scientist found a subject that behaved like a tetrachromat.
For his tests, Jordan used colored discs with different mixtures of pigment, such as green made from yellow and blue. The blends were too subtle for most people: almost everyone saw the same shade of olive green, but each blend gave off a spectrum of light only perceptible to someone with a fourth cone.
Jordan’s subject saw the difference between the clubs. «When a tetrachromat is asked to discriminate between two mixtures, it can do so very quickly. Absolutely,» says Jordan.
Shopping with a tetrachromat
When the extraordinary abilities of the woman found by Jordan were disclosed, the question of many was what do those colors look like?
But she did not want to give interviews. However, the news of its existence caused potentially other tetrachromats to reach out.
One of them is Maureen Seaberg, a journalist and writer from New York.
«I’ve always had disagreements with people about color tones,» she says.
When shopping for clothes, for example, you often find that matching tops and skirts clash because they are different shades and no one seems to notice.
Her sensibility sometimes baffles those around her: once, helping to restore a house, she rejected 32 paint samples before finding the right shade. «The beige ones were too yellow and not blue or cool enough; some of the almond shades were orange,» she recalls. The distinctions that confused the construction company a lot.
This is just anecdotal evidence, but it illustrates a bit how seemingly identical hues can look markedly different to a tetrachromat.
palette and brush
Antico always knew that his eyes saw the world differently.
«When I was little, my mother told me: ‘You will be an artist and an art instructor.'» And so it was: Antico has his own gallery in San Diego, California, where he uses his superhuman vision to create vibrant, color-filled paintings.
Look at the following painting of a rainbow eucalyptus. When compared to the actual tree, the canvas suggests that Antico sees more than the normal eye.
It was upon seeing one of those paintings that a client suggested that Antico contact some researchers who worked on tetrachromatism. The genetic test gave and she began to collaborate with Jameson in a series of positive experiments.
Jameson immediately suspected that Antico’s genes might also be responsible for his increased night vision.
«In his early-morning paintings, he paints with various colors and he does it with very low lighting,» he notes. Under these conditions, our vision is normally reduced to a gray scale.
Jameson’s experiments have shown that to Antico’s eyes, the luminosity of the different colors is half light.
However, extreme sensitivity is not always a blessing.
«The grocery store is a nightmare,» she says. «It’s like a mountain of colors that appears to me from all angles.»
His solace is plain white surfaces. «People think it’s amazing that my favorite color is white, but it makes sense because it’s so calm and soothing to my eyes. While there’s still a lot of color in it, it doesn’t hurt me.»
the path of color
Not all Tetrachromes have such amazing abilities.
For Jameson, Antico’s perception surpasses that of other tetrachromats who have not been artistically disturbed. «Concetta is the perfect storm for tetrachromy because of her experience in perceptual learning as she works with color on a daily basis.»
If that is confirmed in further research, Antico hopes that she, too, will be able to develop a training system for tetrachromatic girls to develop their potential.
But his ambition goes further. Antico believes that he could help people see the world in a different way.
Anecdotally, he says that some of his students have started to notice some extra tones for themselves.
«It’s like a curtain lifted.»
Without genes we will never be able to achieve full tetrachromatic vision, but perhaps people like Antico can point us to some differences that we can only perceive with training.
«What if tetrachromats could show people who are less fortunate the path of color?» he says. «I want everyone to see how beautiful the world is.»
Read the article in English on BBC Future