Since a couple of your illustrations feature slaves who are obviously African, it is important to note that the Romans did not associate slavery with any particular skin color or ethnicity in the sense that we in the United States tend to do because of our particular history. In a negative sort of way, the Romans were not racist: a slave may have been black, brown, white, or whatever, but was a slave regardless of race or skin tone and was considered to be beneath the lowest free Roman.