Jokerule

In the classic origin story, Joker got bleached permanently by jumping into a vat of chemicals, trying to escape Batman as the Red Hood. The Killing Joke despite its flaws was a good take on the story. (Skip the first half if you get the animated version).

But yes, I like this take that the chemicals didn't actually do anything, and he was looking for justification to give his internal id expression.

Yeah, I was about to say, this is literally the plot of The Killing Joke.