> To make it simple: some folks have blue eyes, some brown. Does anyone think that is an adaptation?

Yes.

It is common knowledge that eye color is part of a very basic adaptation to a basic factor in one's environment - sun exposure and UV radiation.

Eye color is pigmentation of the iris, which helps control the amount of light that can enter the pupil. 

The genes associated with eye color are part of the group that control melanin. Eye color is directly related to the amount of melanin in the front layers of the iris. 

People with brown eyes have far more melanin in the iris than people with blue eyes.

Melanin blocks UV for peoples who evolved nearer the equator, so they have both darker skin and darker eyes.  Those of us who evolved far from the equator have far less melanin, as blocking too much UV would make us deficient in vitamin D.

The upshot of all this is that us blue-eyed freckled people have an average UV tolerance only slightly better than that of a vampire, while people with darker skin tones who move north need to drink their milk.

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