Homer Barron is first described as a

Yankee -- a big, dark, ready man, with a big voice and eyes lighter than his face. The little boys would follow in groups to hear him cuss the niggers. . .

Homer is a construction foreman, so he spends a lot of time working outside. This would account for his deep tan, especially considering the warm weather and frequent sunshine of the American South. Further, it would be unlikely to have a black man in a position of such authority at this point in time. The fact that he is described as cussing at the black men who work for him also seems to indicate that he is not a black man himself; if he were, I am sure that he would be described more specifically. In this story, Faulkner identifies black people by skin color (like Tobe), so I would think he'd say so if Homer were black.

That is an interesting idea to speculate about, but given that Faulkner has no problem telling us that Tobe is black, it is highly unlikely that Homer would be so also without Faulkner's saying so.

Remember that the story is set in Mississippi in the late 19th and early 20th centuries. Their relationship was scandalous and caused gossip just because he was a Yankee. There is absolutely no way an African American man could have courted a southern aristocratic white woman without being lynched. The townspeople even gossip about whether Emily and Homer have secretly married because she buys a man's brush set and pajamas. If they wouldn't have tolerated the couple's riding around town in a carriage together, they would have all been downright apopletic about a mixed marriage.

When you read stories like "A Rose for Emily," you can't place today's morality and social values on them--although that would make a great essay topic.