The Blending of Skin Colours

The distinction between such drastic skin colours was more obvious years ago. Without automobiles, planes, and trains, people didn't move around as much. They mated with people from the same areas passing their traits down from generation to generation. Since they were isolated, most of the skin colours were similar.
As technology increased and travelling became accessible people started mating all over the world. Someone that once lived in Africa could move to the north and mate with a light-skinned individual. Skin pigmentation is passed on as a blend, where a number of different shades could result. When two ethnically diverse individuals have children, the children may not have the exact same coloured skin.