My half-sister is lighter than Halle, and she has two black parents. My stepmother is even lighter, and they have no recent white ancestors. I don't believe in the one-drop rule, but perception=reality. Keanu, mentioned in this thread, is considered white, mostly because he looks white. You saw several posters surprised to learn that he is half-Asian. Who here is surprised to learn that Halle is half-black?
Again, it depends on where you are raised. Where I come from, we have alot of folks from Puerto Rico, Dominican Republic, and Brazil that look alot like Halle (although rarely as attractive, at least in NY/NJ). Lots of race mixing down in those places, yet such folks are not considered black up here.