Well, according to Wiki, St. Augustine’s father was named “Patricius,” (LOL what an original name) and was also Pagan. So, considering his Latin name, how being Pagan in in the Roman Empire was really popular, and that St. Augustine was born in a Roman colony; I think that Patricius would have been fair skinned.
And, many people on this thread have pointed out that his mother , St. Monica, is of from the Berber ethnic group. So, mixing those two together (a fair skinned Southern Euro with a West of the Nile Berber), I think you’d get something from your dark-olive Berber, which we see today in Egypt, to a light-tan skinned person, which is type of ethnic group seen across Southern Europe (like in Spain, Italy, Greece, etc.).
But, I highly doubt he was black, as in the the common black ethnic group when we think of as “the Africans.” Those ethnic groups would have been more densely populated (if not, only) on the other side of the Sahara.