A lot of media representations of life in Rome, like Gladiator or Spartacus makes the Empire appear cosmopolitan. Not all non-Romans are slaves, some are merchants, some are seemingly in a upwardly mobile or in a minimally socially comfortable position for the time.
The formation of race (and of chauvinism and supremacy) today was due to factors related to colonialism, surely that dynamic was present in Rome, albeit of a different form. What were race relations like in Ancient Rome?
Could you specify what you mean by race?
There's going to be room for more, but check out:
http://www.reddit.com/r/AskHistorians/comments/19dgfv/when_did_the_concept_of_race_begin_to_emerge/
The Apostle Paul's letter to Titus, who he had left to oversee the church in Crete reflects a fair amount of ethnic prejudice:
"For there are many rebellious people, full of meaningless talk and deception, especially those of the circumcision group. They must be silenced, because they are disrupting whole households by teaching things they ought not to teach—and that for the sake of dishonest gain. One of Crete’s own prophets has said it: “Cretans are always liars, evil brutes, lazy gluttons.” This saying is true. Therefore rebuke them sharply, so that they will be sound in the faith and will pay no attention to Jewish myths or to the merely human commands of those who reject the truth." -- Titus 1:10-14
The formation of race (and of chauvinism and supremacy) today was due to factors related to colonialism
Hah, you can find the exact same views expressed by the Hellenes (Xenophanes and Galen in particular comes to mind), the Arabic Caliphate (look up the term 'zanj' and 'mawali'), the Spaniards ('limpieza de sangre'), etc.
As for the Romans I would recommend simply reading translated primary sources such as letters between citizens (citizenship incidenally being a quite telling subject as it was tiered disallowing most vassal state people's anything more than the 'latin right') since quite a lot of revisionist pop-history readings projecting multicultural ideals upon them evaporates under such scrutiny.