Dear Andrew,

The human eye can see millions and millions of colors. But believe it or not, some colors exist in our world that the human eye can’t see.

That’s what I found out when I went to visit my friend Rachna Narula, an optometrist at the Washington State University Vision Clinic. Using a special camera in her office, she took a picture of my retina, the part in the back of the eye that helps us see color.

Screen Shot 2016-07-07 at 9.05.40 AMSeeing color requires light, she said. When light comes into the eye, it travels to the retina, bounces around, and triggers certain nerves. This sends a signal to your brain. The brain helps translate this signal into an image. In fact, the brain actually plays a big part in how we see color. When you were a baby, your brain was still developing and so was your color vision, Narula said.

Narula explained that humans don’t typically develop full color vision until they are about half a year or so old. Scientists generally agree that babies can only see about eight inches in front of their faces. It’s a pretty blurry view, too. Babies’ eyes are more likely to pick up on black, white, and shades of grey, rather than colors.

But as the brain and eyes develop, they start to pick up on more color differences. The retina in the back of your eye has millions of tiny parts called cones. There are three kinds of cones typically found in the human eye: red, blue, and green.

It’s these three kinds of cones that work together and allow you to see millions of colors. If a person is missing one kind of cone or all of these kinds, they might have a kind of colorblindness. Scientists also think there might be a fourth kind of cone, Narula added. But they are still investigating to find out for sure.

Of course, we can’t know exactly what colors babies or other animals see because they can’t tell us. Instead, we can use what we know about the eye and cones to put together an idea of how it all works.

We cats have red, blue, and green kinds of cones, too. Dogs have only two kinds: one for blue and one for yellow. The mantis shrimp, with their rainbow-patterned exoskeletons, have 16 kinds of cones. This particular shrimp can even see certain kinds of ultraviolet light that humans can’t see. Different kinds and numbers of cones can give animals vastly different experiences of how they see the world.

After all, even a single color can change depending on the lighting, shadows, or environment. Who knows—maybe one day you’ll invent a color counting machine and we’ll be able to get an even better estimate of how many colors exist. In the meantime, pull out the crayons or mix some paint. Dr. Narula and I would love to see what colorful things you can create. Send in a picture for a chance to have it featured right here on the website.


Dr. Universe

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