Redheads are probably less genetically diverse than the rest of the population, iirc it’s mostly caused by a recessive gene. So if someone is a redhead, then the chances are high that they share other special genes with other redheads.

Africans on the other hand are more genetically diverse than people from other continents. It’s possible that some African population groups require different levels of medications, but you won’t be able to tell those population groups apart by the color of their skin.