There are reports of black legionaries in Romain Britain as late as the reign of Septimus Severus (himself not very white if you look at portraits).
Black people in the Roman empire isn't that far fetched when you consider Rome had a huge presence in Africa and the Trans-Saharan slave trade was thriving at the time. Rome also had contacts with Merowe (Kush) through Egypt and other client kingdoms in North Africa. It's not a stretch to imagine a small but steady stream of black slaves (possibly manumitted later), mercenaries and merchants trickling into the empire and spreading throughout, especially when one considers that the military was one of the very few social advancement possibilities if you weren't already from an aristocratic or at least land-owning family (Rome would give veterans a money payout equal to all of their 20+ years' service arrears plus a bonus and Roman citizenship at the end of service, allowing one to retire in relative comfort).
So they wouldn't be as frequent as in the US, but they definitely wouldn't be an oddity either.
Black people in the Roman empire isn't that far fetched when you consider Rome had a huge presence in Africa and the Trans-Saharan slave trade was thriving at the time. Rome also had contacts with Merowe (Kush) through Egypt and other client kingdoms in North Africa. It's not a stretch to imagine a small but steady stream of black slaves (possibly manumitted later), mercenaries and merchants trickling into the empire and spreading throughout, especially when one considers that the military was one of the very few social advancement possibilities if you weren't already from an aristocratic or at least land-owning family (Rome would give veterans a money payout equal to all of their 20+ years' service arrears plus a bonus and Roman citizenship at the end of service, allowing one to retire in relative comfort).
So they wouldn't be as frequent as in the US, but they definitely wouldn't be an oddity either.