I know that the Romans are famous for incorporating conquered peoples into their empire, but when they saw people that didn't look like them, did they have any preconceived judgements?
Hi, hopefully someone can drop by with an answer particularly wrt slavery, but meanwhile, you may be interested in a few earlier discussions
FAQ section Pre-History of "Race" and Racism, particularly the following
Racism in the ancient world? featuring /u/einhverfr
How would I be treated in Ancient Roman as a black man? featuring /u/Tiako
Did the Greeks and Romans hold any racist views towards their neighbors?
It was based on class, not race. At the top of the pyramid were Romans who held the full citizenship. If you held the citizenship and observed Roman culture, you were automatically above the freedman and slave classes. It is possible for a black man to obtain the citizenship; he could be the son of freedmen an example (children of freemen were granted full citizenship). In that case, then he would be regarded as higher than say- a Gaulish socii (a step beneath full citizenship) -. Also remember that Rome was a multi ethnic Empire so foreigners were not unheard of. Egypt was a Roman province, as well as a wide swath of North Africa. The idea of whether or not you were "Roman" was more important.