Why is the human eye colour generally Brown, Blue and other similar variations. Why no bright green, purple, black or orange?
In: Biology
In short the same reason why *human skin isn’t anything else but light to dark brown and also the same reason why *human hair is naturally certain shades of one another like brown, blonde, black, red, etc. It’s because of a natural pigment group of amino acids called melanin that is the pigment in most living organisms. When is comes over to eye color, blue means no melanin in the eye, and when light particles get absorbed they gets scattered back into the atmosphere. Eyes with a little bit of melanin are green to hazel and eyes with a lot of melanin are brown to dark brown.
Didn’t Elizabeth Taylor have purple eyes?
Edit: thanks for the silver kind stranger!
Eyecolor is determained by the amount of melanin in the iris. Melanin is a darkish pigment that helps protext the skin and eyes by blocking damaging UV rays.
The color comes from how light is refracted in your eyeball with the melanin. Blue eyes have the least amount, leading to the color blue being reflected mostly, in a processes similar to how the sky is blue.
More melaanin causes more brown tones, leading to green with a little more, and greys and growns with other amounts.
The way light reflects with this pigment doesn’t allow for purple or other colors to show.
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My wife tells me that my eyes switch between being green and blue, which I always thought was interesting. Why would that happen?
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Humans do have a full rainbow of eye colors! Some colors are just very rare, and not necessarily healthy for an eye to have. Here’s what humans naturally have in increasing rarity:
Black / brown – caused by a brown chemical (melanin) at the back of the iris. Black eyes are just really dark brown.
Hazel / amber / yellow – caused by a yellow chemical (lipochrome) and melanin at the back of the iris
Blue – very little if any pigments in the eye. There is a clear squishy layer that reflects blue better than other colors (Tyndall scattering). The thickness of this layer can affect the brightness of the blue. Most irises would have this blueness if there is no melanin. Newborn babies sometimes start with blue eyes before they become pigmented.
Green – amber pigmentation, but not much. The blueness of the iris also shows through. The colors mix and make green.
Grey – no pigmentation like blue eyes, but the clear squishy layer is too thin to reflect much blue light. The iris’ opaque whitish color shows (kinda like the color of the whites of your eyes). Another variation is there is something goopy (collagen) that absorbs a little bit of every color. We’re still trying to figure out this one.
Red – blue or grey eyes where there is little to no coloration, and the red blood vessels show through. This is usually not healthy.
Purple / violet – red eyes that still have a little blue coloration left. Elizabeth Taylor famously had this eye color.
Why no neon colors? – human bodies simply don’t have a lot of pigments to put into our eyes. It’s kinda like mixing paint, and we only have brown and yellow. Our bodies sometimes do tricks with blue and grey, kinda like putting paint on white paper with harsh lighting to make another color sort of appear. For some, like neon green, you can’t get that color without a neon green paint. Just biology there.
Thanks for the replys everyone. Would people care to share any photos of their eyes? Close ups obviously to preserve anonymity etc even if your eyes aren’t an off colour I’d just be interested to see the differences.
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