Nonsense. Had Hermione not been white, that would have been mentioned somewhere in the books or films. It was never mentioned. Rowling consented to having a white actress play the character in the films. Those facts explains the mental image that Rowling's fans have of a white Hermione. It is precisely the image that Rowling intended. To suggest that Rowling's fans are racist for having the image is obscene.
However, an adult Hermione can certainly be black in the play. The Harry Potter works are not just fiction, they are fiction about magic. Magic can easily explain a skin color change. However, to retain continuity with previous works, the skin color change MUST be explained.
Why do leftists feel morally superior when they label non-racists as racists?
Prisoner of Azkaban page 59
This is all Rowling's pandering to the PC crowd to make herself fell good about her self righteousness. First Dumbledore being gay and now Hermione. What's next, Harry is really Bruce Jenner in disguise?