How could a human like species adapt to change colour?

So in my world I've got a mostly human like species but they've evolved to camouflage, specifically colour change. The world is an earth-like medieval fantasy. The different parts that appear to change are:

Hair: They can change the colour of their hair (including body hair) at will, takes a couple of seconds.

Eyes: Doesn't actually change but are reflective so they appear to be whatever colour is most prevalent.

Skin: Cannot be done at will or controlled, instead changes over the course of 1-2 months depending on trends in temperature and humidity. So that their skin colour matches the kind of environments. e.g. hot and humid = brown skin, hot and dry = sandy skin.

How could these adaptations come about and how would they work?

posted over 6 years ago

ArcWraith‭

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