The colour bit's simple to understand, nowadays it's not the problem it used to be for people with dark skin, black even, but in times past the darker skinned people wouldn't have been manufacturing enough vitamin D, and would have been suffering from rickets and all of the associated disadvantages, due to the lack of photosynthesised vitamin D where the weaker sunlight found it more difficult to penetrate the skin of darker people, evolution then took over and favoured lighter skinned people that wanted to live in the more northerly climes and that's why we're the now so called white people, it was just down to survival.(I'll end up with a permanent train spotters voice if I do any more of these explanations, like the Did you know voice of Peter Cook's).
Regards ippy