If I understand you correctly there were two migrations out of Africa one was the white race the other was the black race
am I correct in saying that?
Instead, the Sen people arose from a Homo Habilis population in Western Asia. They then got a yen for travel and went Souf', North, East and West ~ the Sen still exist and live in South Africa.
Their descendants live back up the trail.
"White" has arisen maybe three times ~ with Neanderthals, with Europeans, with East Asians. In all cases the condition happens in areas of reduced incidence of sunlight and is believed to be rather recent (as this sort of thing happens).
Light skinned East Asians are made "light" by a different set of genes than light skinned Europeans, or light skinned Neanderthals. I have no doubt that when "they" are done with their analysis and categorization of DNA genes and the external epigenetic controls they'll find a number of ways extra melanin gets produced.