Somalis and Ethiopians are not mixed with Arabs and you have plenty of light skin west Africans. Who uses caucasoid? Africa has the most diversity in skin tone and facial features than any place in the world. Most AA's are mixed with European and black anyway
Ethiopians (East Africans) and Yorubas (West Africans) have radically different genetic profiles, Ethiopians being 1/4 to 1/3 Southwest Asian in ancestry, which means from the Arabian peninsula. The rest of their ancestry is East African, which means dark skinned but with different features from West Africans.
Africa is huge, there are people from different places in Africa that look very different, but Africans in any given country or region within a country look very alike. There recently was outrage in france because an adventure game on TV had a challenge that consisted of finding a specific kid among hundreds in a West African school playground, so as you can imagine all the kids looked the same to the untrained French eye, no kid had any outstanding feature that would strikingly set them apart from the rest, they could not focus on searching lightskins or darksins because all kids nearly had the same dark skin tone, black hair, dark eyes and same uniform. It took them hours before they found the right kid after failing 20 or 30 times.
As a Haitian I was not shocked at all, we all look similar, like a big family, and one needs to be accustomed to black people to notice the differences we see among each other. If I had to find one specific Japanese child among hundreds, I'd be just as confused, because East Asians also have very low diversity in skin tone and facial features. Light skin is so foreign among black people that Bob Marley while growing up in Jamaica was bullied and called a white boy due to being half-white due to his English father.
This is a crowd in Senegal, nobody is light-skinned, it's just how it is, there's never been mass migration of light-skinned people here and melanin protects skin from sunburns under these lattitudes. African-Americans look the way they do because at some point in their genealogical tree they had people looking like these men above who had children with people looking like Donald Trump or Pochaontas, not because they had African ancestors that looked like Drake.