it is called envirnment and you can have an asian female have for of the same DNA markers with a white women than an asian man. Skin color only has to do with pigmentation and the amount of vitamin d your ancestors needed to absorb. Take sociology race and ethnic relations, it will explain it all.
The only reason people from african orgin have more of a chance of getting cycle cell anemia is because their ancestor developed an immunity to malaria and so on.
Environment is certainly a factor, but we are talking about groups of people that have been relatively isolated from one another for thousands of years. Take for instance, Asians. Now, sure, their skin color, body features, etc., are different from other races, but could it be possible that their brains are wired up differently from other races as well? I'm not saying this is good or bad, right or wrong, that they are smarter or dumber, etc. I'm just considering the possibility that there might be differences in brain function between races, whatever those might be. Unfortunately, this type of research is frowned upon by the world community, so there is a very limited amount of data.