As long as Sue is black as well, or he's adopted and she's the kid their parents turned out to be able to have after all even though they adopted because they thought that they couldn't have biological kids, or mayeb both of them are adopted, or some other explanation is offered for Sue's race being different, I don't see a problem with this.
Look, people:
1. His ethnicity doesn't have any real importance to his character. Changing
2. "I just want them to stay visually true to the source material!" Right... I didn't hear anybody complaining about Ben being bald in the original movies. Or about Johnny's hair being much shorter and a different color. So visually speaking, it seems like people are perfectly fine with visual changes to the characters as long as they all remain of the caucasian persuasion.
3. Whenever you make a movie you need to make changes. You can't have everything be exactly the way it is in the movies, or we'd have a big-screen version of Fantastic Four #1 and onward complete with bombastic narration by Stan Lee. And people generally accept that a movie can't be exacly like the comics.
Unless you pick a black actor, in which case people start complaining like crazy.