Why do North Europeans and Turkic people have a variation in eye colours (blue, green, gray, etc.)?

Question

And the rest of the world has more or less brown OR black eyes?

Answer 1

Because northern Europeans and Turks are related populations from the same area of central Asia.

A mutation happened in this region and spread through the population.  This area has reduced sunlight compared to Africa, so lighter colored eyes were no disadvantageous.

Answer 2

Our ancient ancestors came from places with dimmer sunlight.  More light comes through the lighter colors.

Lighter skin also allows deeper light penetration to provide enough vitamin D.

Answer 3

And you know this... how?

I think eye colors in the world today are pretty well mixed up.