eye color and skin color

[ttyo888]

Hi I just noticed that the eye color of mammals and humans seem to have a wider range of colors then skin and fur of mammals.

 

So I m wondering can mammals if possible produce purple hair or green skin the same way as the eyes of some animals?

 

Blue Skin is well known in some mammals

 

Discuss.

[Moontanman]

I don't think there is a connection between blue eyes and blue skin. Blue eyes is more from a lack of pigment than actual blue pigment at least in humans.

[Mokele]

Maybe mammals simply lost some of color pigments during their evolution. They do seem curiously dull compared to other vertebrates.

[ttyo888]

then explain the blue skin of some mammals like the mandrill?

[Mokele]

Re-evolution of the pigments, perhaps?

[ttyo888]

Hmm then what about the fur/hair? Maybe the same Rayleigh scattering can be applied to them?

[changizi]

Actually, human skin can become *any* color. Your skin can shift along a red-green dimension as the oxygenation of your blood shifts. And your skin can shift along a blue-yellow dimension when there is more or less blood in your skin. Every hue is thereby obtainable.

 

That's all the hues on a *single* animal's skin. But perhaps your questions concerns the baseline skin color of a species. There are a heck of a lot of baseline skin colors across primates, although whether it is more or less than that of the eye colors, I'm not sure.

[Mokele]

Um, no. Yellow skin in humans is caused by jaundice and the buildup of toxic metabolic byproducts. Green, as seen in bruises, is also due to toxic metabolic byproducts and the body breaks down damaged tissue.

[ttyo888]

what about hair?

[changizi]

Um, no. Yellow skin in humans is caused by jaundice and the buildup of toxic metabolic byproducts. Green, as seen in bruises, is also due to toxic metabolic byproducts and the body breaks down damaged tissue.

 

You're right that jaundice can make skin yellow. And, true, bruises can make it skin green (although bruises also lead to a sequence of colors as it heals).

 

But normal healthy skin can modulate along the two opponent dimensions of color (red-green, and yellow-blue).

[Mokele]

But normal healthy skin can modulate along the two opponent dimensions of color (red-green, and yellow-blue).

 

No, it cannot. Your skin's apparent color can become paler, redder, or bluer depending upon blood perfusion and oxygenation, and your skin can darken in response to UV exposure (tanning).

 

There is no healthy way for skin to be yellow or green.

[changizi]

Slightly talking past each other. Although blood perfusion modulates skin along a yellow-blue dimension and oxygenation modulates skin along a red-green dimension, the actual color one perceives on a spot of skin depends on the spectrum of the skin nearby. For example, veins appear blue-green to the eye, but are not "truly" blue-green in the sense that if you view veins through an aperture such that no surrounding skin is perceptually adjacent to it, it appears skin colored, not blue-green at all. I'm concentrating on the "dimensions" of color modulation, rather than the perceived color, because the perceived color is more context dependent. So, for example, you're right that red is a color signal humans show much more often than green; but this is because we have color-signaling mechanisms that shift one spot (like a cheek) to be relatively more oxygenated, and so the spot looks redder relative to the unchanged nearby skin. If, instead, the surrounding skin were to everywhere shift redder but leave that spot unchanged, then that spot would be appear green. But the latter doesn't appear to be something our skin does, so we don't typically see green. (Except over veins.)

 

For the blue-yellow dimension, we do see both quite often. But blood perfusion does not only change the hue, but also simultaneously modulates the lightness. So as it yellows it also lightens, and as it blues it darkens. (Unlike for the oxygenation dimension, which is fairly equiluminant as it modulates.) Squeeze blood out from your palm, say, and it will become yellower. (...and lighten.) And more blood makes it bluer (and darker). E.g., your veins have more blood, and they are bluer (and also have a green shift because deoxygenated). Also, a brief tourniquet on your hand, say, will make it bluer (but this time with a red shift because it is relatively oxygenated as well, so purpler in all). (And note that the color difference between veins and the tourniquet case is a red-green one, because the main difference between them is one of oxygenation.)

[ttyo888]

Blue skin has appeared in some mammal groups... like the mandrill's face for example based on an article they say that there are some collagen fibres causing a Rayleigh scattering in the skin of the mandrill