Not long ago I read about Vervet monkey. Here's picture:

enter image description here My question is what causes this blue coloration of the scrotum? I don't mean evolutionary need (e.g. attracting females), but what pigment or other factor is responsible for this color?

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    $\begingroup$ I've suggested an edit to your post; in the future please upload pictures rather than including links. Links are discouraged since 1) if they break they no longer add value to this post, and 2) they can be used to link to malicious websites. Thanks! 😊 $\endgroup$
    – tyersome
    Nov 29, 2019 at 23:16
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    $\begingroup$ A related question about blue food that doesn't answer your question, but you might find it interesting: Why are so few foods blue? $\endgroup$ Nov 30, 2019 at 17:22

1 Answer 1


Blue coloration in animals is caused by structural color rather than blue pigments. In the case of vervet monkeys and other mammals studied this is due to collagen fibers in the skin being arranged with a regular spacing that results in blue wavelengths constructively interfering while other wavelengths destructively interfere1.

This "news" article in Science discusses this phenomenon and mentions Vervet monkeys.


1: Prum, R. O., & Torres, R. (2004). Structural colouration of mammalian skin: convergent evolution of coherently scattering dermal collagen arrays. Journal of Experimental Biology, 207(12), 2157-2172.

  • $\begingroup$ Excellent! (+1). It's always nice to see such useful primary literature cited here on Bio.SE! Can you elaborate a tiny bit more from the paper (i.e., describe the tissue arrangement more explicitly etc.)? -- Not necessary, but I think doing so would make the answer stand better on its own (in case links died and someone can't get access to the paper). $\endgroup$ Nov 30, 2019 at 17:32

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