Personally speaking, I always imagined her as White (even though I read the books before watching the films). This is not to say that she isn't Black, but this is personally what I imagined. Also, the following line (from PoA I believe) has gotten popular online:
"Hermione's white face" could be considered as proof that she was White, though there is the part where she is noted to look "very brown."
Also, IIRC, the summer between CoS and PoA, Hermione went on vacation, so maybe the "very brown" line was a reference to her being tanned? Idk