Not to mention which, former slaves became Roman citizens, took their masters’ names and became their masters' “clients,” with the obligation to support them politically and practically. Having a large client base was very important for elite Roman men and reportedly a very strong motivation for manumitting slaves who were likely to become productive members of society.

Obviously, this was most useful to literate Greek slaves like pedagogues who often entered into slavery voluntarily for a shot at the coveted citizenship.

Unskilled agricultural and mine workers outside the city of Rome didn’t fare so well. Except for those who worked in small family operations, those sorts of slaves were often worked to death and never had a shot at manumission.

Evidence shows that at least in the first century CE the bulk of slaves mistreated in this way were Gauls or Germans. Darker skinned people in that era tended to be more educated.

But then nobody would have thought of it in those terms, because race did not exist as a concept and dark skin did not seem to be stigmatizing. The first few emperors after the Julio Claudians, for example, seem to have had pretty dark skin. The celebrated Emperor Hadrian, if he popped into society today, would probably not be considered a white man.