By definition black face is racist. "Blackface is a form of theatrical make-up used predominantly by non-black performers to represent a caricature of a black person. It is a racially insensitive representation of the African American community. However these fools better not use it too liberally other wise all it's meaning will dip like a stalling airplane.
Is it racist if an African girl dresses as Snow White? No. Is it racist for a Caucasian boy to dress as Aladdin? No. Is it racist for an Asian boy to dress as Chuck Norris? No. Is it racist for an Asian girl to dress as the Little Mermaid? No.
It could be racist if meant to make fun of or demean Africans. But other than that i don't see how wearing blackface for lets say, A play, Is bad. Whether its racist or not completely depends on how its used and isnt inheritely racist. . . . . .