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SciShow explains the genetics -- and physics -- behind why blue eyes are blue, and what the future may be for the trait. Spoiler alert: Blue eyes aren't really blue! SciShow explains!

The eyes may be the windows to the soul, but they're also the keepers of all kinds of secrets-secrets our eye doctors are in on but we typically aren't. Those little tidbits of info our baby blues (or greens or browns) are hiding are actually chock-full of important details, not only about our eyes and vision, but about our overall health.

This indicates that the mutation originated in just one person who became the ancestor of all subsequent people in the world with blue eyes, according to a study by Professor Hans Eiberg and colleagues at the University of Copenhagen.

Normally, male squirrel monkeys can't distinguish between red and green hues-they're what is called color-blind in humans. The South American Saimiri genus lacks a gene that allows color-sensitive cells in the eye, called cones, to differentiate red and green from gray. To these animals, other colors, such as blue, brown and orange, appear faded. But Sam was one of two males in the experimental group of a groundbreaking 2009 ophthalmological study conducted at the Washington National Primate Research Center in Seattle. Husband-and-wife vision researchers Jay and Maureen Neitz injected a viral vector behind the retinas, the part of the eye that responds to color, of Sam and his simian lab partner, Dalton. The virus contained the genetic code in human eyes for red pigment, giving the monkeys an extra class of cone photoreceptor.

We see color because of specialized light-sensing cells in our eyes called cones. One type, L-cones, sees the reds of strawberries and fire trucks; M-cones detect green leaves, and S-cones let us know the sky is blue. But vision scientists have now discovered that not all cones sense color (see video).

3 minute video Each father and mother pass down traits to their children, who inherit combinations of their dominant or recessive alleles. But how do we know so much about genetics today? Hortensia Jiménez Díaz explains how studying pea plants revealed why you may have blue eyes.

hat is color blindness? A color festival. No. Color blindness or color deficiency is a vision problem. Now, our eyes have light sensitive cells called rods and cones. Can I put ice cream on these cones? You are just unbelievable. Rods are responsible for black and white vision. They do not detect color. Whereas, cones detect color. There are three types of cones. One cone perceives red light, another perceives green and the third perceives blue. Together, these cones help us to see the whole spectrum of colors. Now in some cases, when one or more types of cones do not work properly, it causes color blindness. People with such deficiency have difficulty in distinguishing between certain colors or shades. For example, in red-green color blindness, the apple tree may appear like this.