I agree the poster who said it is normal that the Black cultures/characters die out too often in games. This is issue particularly with the Ethiopians (due to Fatimids politically invading and eventually culturally replacing them) but sometimes this happens in Mali, too. Sometimes it's the Almoravids or other Moors but usually Castille/Léon, France or HRE who ends up conquering Mali and gradually replacing the Black cultures there.
Usually it leads to exiled Black courtiers in Christian Europe which is totally plausible to me. I guess that was the complaint of the OP. It shouldn't be a problem even if you are a racist, because the African features will usually die out in a few generations.
I try usually marry the exiled courtiers and educate them in my culture and eventually give them land. It's fun to see for example the Zagwes or Godwinsons survive this way. In my current game as Count-of-Vannes-turned-King-of-Britanny I had a short Norwegian adventure which resulted in my court having a random Yngling. I married him to a black court lady I found in Ethiopian hinterlands. The result in 100 years: I have the most loyal Breton duke of Berry who is spreading the Breton culture in the heart of France. Whose name is Yngling. Who is Black.

Only recently that line has turned white. The reason they remained Black for decades was just pure luck, I guess, because there was no injection of African genes in the ducal line. Some of the ducal children were looking like Middle Eastern but the eldest child got always the African looks...