Actually the question is backwards. All races came from Africa and we divided and some headed north where there was far less sun which made skin turn lighter because of less need for sun protection. Some headed east where the sun was still warm, but not as much, but in the end we all come from Africa. This is proven science.
Skin color is due to geography and evolution. Black folk have dark skin due to the fact that they were closer to the equator. The skin pigments evolved to protect them from the suns rays. At least this is what I was taught many years ago. If it's wrong, would someone with the correct answer respond? I'm interested as well.
I think it varies a lot, possibly native americans, west africans, hispanic and white. Occasionally malaysian *cough* tiger woods *cough*. I don't think many indian/pakistani and black mixes exist though, but could be very wrong.