I had a drama teacher who used to get really worked up when he felt people were using the term blackface wrong.
His opinion was that blackface was what minstrels did with the black greasepaint and exaggerated accented white/red paint to make a person look like a racist caricature of a black person.
While using make-up to simulate the skin tone of a black person (or any other race) was a time honored stage tradition like when a white person was cast as Othello.
I used to piss him off when I would always chime in with: "Why not just hire a black actor to play Othello though?"