The Humans still in Africa are actually more genetically diverse than all the rest of the world put together - if you count just the differences in the genes rather than ones which make a visible change.
The alterations seen in the rest of the world are visible due to the environment - simply getting a small population separated by mountain ranges or rivers can cause genetic oddities to become genetic normalities.
Skin colour doesn't count so much. Mothers with a high exposure to sunlight and so a high amount of melanin in their bloodstream have darker children than those with the same genetic background who live in low sunlight conditions immediately before and during their pregnancy. It is an epigenetic factor.
I was reading about this earlier. Very interesting. Though, I have green eyes. But, it did get me researching hair colour, too (as my natural colour is ash blonde). I'm a very curious person when it comes to science...
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