Most people are trichromats.
Most animals are dichromats.
In some rare cases some women might be a tetrachromats.
Okay, I see you have lost me. I’ll teach you what I myself have just learned.
We see color because of specialized nerve cells in the retina called cones, which function only in bright light. Most people are trichromats which means they have three of these cones to perceive color with. Each cone cell is capable of perceiving about 100 different colors, so the total number of colors a trichromatic person can perceive is 100ᶟ, or one million.
As you can probably guess, most animals are dichromats and have two cones. As do color-blind people who can only perceive 10,000 shades.
Tetrachromats, which include certain fish, birds, and insects, and some humans, have four different types of cone cells. This is a very rare condition and affords the person the ability to see an incredible 100 million colors.
Discover Magazine reported in 2012 that Newcastle University neuroscientist Gabriele Jordan and her colleagues had been searching for people with this super-vision and after more than 25 years finally found one.
A doctor living in northern England, referred to only as cDa29 in the literature, is the first tetrachromat known to science.
The idea that tetrachromats might exist was hinted at in 1948 when Dutch scientist HL de Vries, discovered something interesting about the eyes of color blind people. While color blind men only possess two normal cone cells and one mutant cone that’s less sensitive to either green or red light, De Vries showed that the mothers and daughters of color blind men had one mutant cone and three normal cones, in other word four cone cells. The possibility was that people who possessed an extra cone cell would be able to see a much greater range of colors than the rest of us.
It was only in the late 1980’s that John Mollon from Cambridge University started searching for women who might have four functioning cone cells. Assuming that color blind men pass this fourth cone cell onto their daughters, Mollon tested such women but couldn’t find anyone with unusual color perception.
Was tetrechomats just a figment of scientific imagination?
Then, in 2007, Jordan, who had formerly worked alongside Mollon, tried a different test. She found 25 women who had a fourth type of cone cell, and put them in a dark room. She presented the women with three flashing colored circles that they peered at through a lab device.
To a tetrachromat, though, one circle would stand out because it was not a pure color but a subtle mixture of red and green light randomly generated by a computer. Only a tetrachromat would be able to perceive the difference, thanks to the extra shades made visible by her fourth cone.
When one of the woman was able to distinguish the extra shades, Jordan was ecstatic.
“We now know tetrachromacy exists,” she told Greenwood. “But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.”