http://www.uesp.net/wiki/Lore:Ebonarm. And I've been to North Africa. That's why I didn't mention North Africa. I mentioned Western Africa.
If you 've been to North Africa , then you should know , North Africans are not black at all , they are white for more than 95% of them , except the Sahara Tuareg nomad people

Actually the Redguards in TES lore take inspiration from two things in human real history IMHO :
- The Nubians (Sudan , Ethiopia etc ) at the time of Ancien Egyptians ( Nubians and East Africans in general have different complexion than Western africans , usually slimer traits , like thinner nose , less black , not as bulky on average etc , like the Redguards in game
- the Almoravids/Almohads Black Africans mercenaries or slave warriors that they brought from Mauritania , Mali , Senegal etc.. , who were numerous in their armies that invaded and submitted Spain for several centuries (http://en.wikipedia.org/wiki/Almoravid_dynasty) , people in europe back then would call them Saracens
- the Persian and Arab civilisation for the Redguard culture , fashion , weapons etc..
Well IMHO , just my opinion