In my head Hermione was a bit olive skinned but not of African descent - at one point after her summer in France with her parents she is described as being “very brown” (and Ron is described as being very freckled after coming back from Egypt but that’s neither here nor there) but she is never described as a black person while others like Dean, Blaise, Angelina etc are explicitly stated as such.

I don’t know if Jo was intentionally being vague to have her be relatable or if she didn’t think about it that much or if it’s a retcon now, but you would think if she was supposed to be one specific ethnicity why wouldn’t it be said? Why does it matter at all? She’s a smart, strong female character without a specific box to be put into and that’s okay. Because it’s so vague I think it’s a little rich for others to call it white-washing too - most if not all of the characters specifically described as black are black in the movies too.