When Concetta Antico looks at a leaf, she sees much more than just green. “Around the edge I’ll see orange or red or purple in the shadow; you might see dark green but I’ll see violet, turquoise, blue,” she said. “It’s like a mosaic of color.” Antico doesn’t just perceive these colors because she’s an artist who paints in the impressionist style.
She’s also a tetrachromat, which means that she has more receptors in her eyes to absorb color. The difference lies in Antico’s cones, structures in the eyes that are calibrated to absorb particular wavelengths of light and transmit them to the brain. The average person has three cones, which enables him to see about one million colors. But Antico has four cones, so her eyes are capable of picking up dimensions and nuances of color, an estimated 100 million of them, that the average person cannot. “It’s shocking to me how little color people are seeing,” she said.
Although tetrachromats have more receptors in their eyes, their brains are wired the same way as a person with normal vision. So how can a brain like Antico’s change to see more colors? Like anything else, practice makes perfect, even when it comes to neural pathways. For years, researchers weren’t sure tetrachromacy existed. If it did, they stipulated, it could only be found in women. This is because of the genes behind color vision. People who have regular color vision have three cones, tuned to the wavelengths of red, green, and blue.
These are connected to the X chromosome, men have one, but women have two. Mutations in the X chromosome cause a person to perceive more or less color, which is why men more commonly have congenital colorblindness than women (if their one X chromosome has a mutation). But the theory stood that if a woman received two mutated X chromosomes, she could have four cones instead of the usual three.