“Scientists have found that multiple genes, as many as 16, contribute to an individual’s eye color. Essentially, those genes determine two things: the amount of pigmentation in the iris (the colored part of the eye), and the manner in which the tissues of the iris scatter light.

“Irises that appear green result from a lower amount of melanin (a pigment that absorbs light and creates color), combined with the scattering of  light from the iris, which adds a degree of blue—the same phenomenon which makes the sky and the ocean look blue. A striking example of this effect is the iconic National Geographic cover of Afghani girl Sharbat Gula. At first, it seems certain that Gula’s eyes are purely and distinctly green. A closer look, however, reveals that they actually have a vibrant bright blue exterior, with a center filled in by a light amber-brown.

Photographer Steve McCurry’s ‘National Geographic’ cover of Afghan girl Sharbat Gula.

“This isn’t unusual—other colors are often lurking within green eyes. According to the Martin–Schultz scale, a standard eye color scale used in anthropology, there are 16 different eye colors in the world. One is simply green. The other two that involve green are hybrids: gray-green with yellow and brown spots, and green with yellow and brown spots.

“But those are just the ways of describing the color that we perceive one’s eyes to be. The only actual pigment found in human eyes is melanin, which is brown; the rest of the color spectrum results from the light-scattering effect.”

To continue reading this fascinating Daily Beast article, click here.