Why do our eyes see in color? Neuroscientist Mark Changizi examines this question in his book The Vision Revolution. He says that the human eye evolved to see colors in part to glean what another person feels by detecting subtle color changes in their skin. He told EarthSky:
One of the most important things in our lives is other people’s faces, and the skin on those faces. The brain really cares about seeing the small differences.
He said color changes that happen on our faces – like blushing – reveal a lot about people.
You can discern a lot about what’s going on in their brains, what their mood is, what their state is, what their current emotion is.
Changizi added that being able to see colors can also clue people in to the health of others.
In the medical communities, they’ve long used color within the symptomology within certain diseases. And if you’ve ever had a kid, they’re color-changing all the time. When they clench to fill their diaper, they’re immediately purple. Their face is brilliantly purple. Every little thing that they do, their faces are changing much more quickly. Much of this is medical related, and much of this is emotion related. But more generally, the idea is that it gets you a view into the underlying state of another human.
Changizi said the human eye has a particular part that enables us to see these subtle color changes. Dogs, for instance, can only see blue, yellow, black and white. They lack the receptor, or cone cell, for seeing red and green. He said:
As I looked into it, I was able to work out, on the basis of oxygenation of hemoglobin that underlies these changes in your skin, what would our cones have to be like to be able to sense the oxygenation and de-oxygenation of hemoglobin.
It turns out you have to have a really peculiar type of color vision, one where you have a new cone that’s almost just like one of these mammalian cones, it’s almost in the same spot, but a little shifted over. You have to have cones like that in a peculiar way, in order to sense the spectral changes that happen on the skin, or to see the emotions of others, you have to have the funny kind of color vision that we have.
Listen to the 8-minute interview with Mark Changizi on why our human eyes see color (at top of page).