Well I saw this thing that talked about how some actors who played superheroes were Hispanic or something like that. Dean Cane, Linda Carter, etc. So I guess as long as they look like the character in the comic people wont really care. I don't know. It wouldn't bother me if they did that.
Billy D. Williams almost played Two-Face, and he did play Harvey Dent in Batman 1 by Tim Burton. I was upset when I heard that Laurence Fishburne was going to play Doc Ock in Spider-Man, but not because of his race really but because he wasn't this older heavy German (because of the cartoon I thought Ock had a thick German accent) man. But if he had put on the weight and started using a thick German accent I think I would have been fine with that. I would have been fine if Donald Glover actually was going to play Spider-Man/Peter Parker because he could portray Peter as the silly nerdy guy he is. I didn't care that Kingpin was played by Michael Clark Duncan in the DD movie and when I heard Cuba Gooding Jr wanted to play Murdock I thought that might have been really cool.
I think its more like the comic fans get upset if the character, story, look, differ too much from the comic. People got upset that Spider-Man used organic web shooters, or that Joker didn't look like the comic when Ledger played him. I hope its just along that line of thinking and not reaction to their race.