Alexa Tsoulis-Reay, for New York magazine:

Tetrachromats can see colors that most people cannot — up to 100 million, estimates suggest, which is 100 times that of the average human. Most people have three cells, or receptors, in their retinas, but tetrachomats have a fourth receptor, which may be what allows for their heightened color perception. They are usually female, and it’s estimated that about 12 percent of women carry the gene for this fourth receptor. Carrying the gene doesn’t guarantee that you’ll wind up with heightened color vision, but those who both have the gene and who are immersed in a wide range of colors from a very young age appear to be more likely to develop the ability. Researchers are still in the very early stages in their understanding of this condition, so there aren’t any hard numbers on how often it manifests itself.

This article about Concetta Antico is not only fascinating, it is also extremely inspiring. What I found most amazing, is how well Concetta describes the colours that she is able to see — it must be fascinating to see everything around us the way she can. My first thought was that I am blind in comparison to her — just read her description of the colour of grass:

Let’s take mowed grass. Someone who doesn’t have this genetic variation might see bright green, maybe lights or darks in it. I see pinks, reds, oranges, gold in the blades and the tips, and gray-blues and violets and dark greens, browns and emeralds and viridians, limes and many more colors — hundreds of other colors in grass. It’s fascinating and mesmerizing.

She can also tell when someone is sick by just looking at the colour(s) of their skin.