When Jack first becomes the Joker, and he rips the bandages off of his face, says his famous mirror...MIRROR!!! line, breaks the light and the mirror and goes up the stairs laughing, he steps into the light for a very brief second right when he reaches the top of the stairs. When he does you can see that his face isn't white. It's normal skin color. I guess the producers thought it would be a waste of time to put on all of that makeup for a scene that was MOSTLY in the dark. But we Caught em.