Sure, but in a world dominated by the Christian church, isn't it possible that the discrimination was based more on religion than on race?

I don't remember where (help me, please!) but I read an account by a medieval European monk visiting monasteries and Christian communities in Africa. He described their religious practices, traditions, culture architecture and food in great detail, but mentioned their (certainly much darker) skin tones only in passing.

"Race" (boiled down to skin melanin contents) as a distinguishing point between groups of people is not a permanent fixture in human history. It is especially overwhelmed by religion, language and culture/tribal nationality in terms of its use as a dividing point between "us" and "them".