tgva8889 asked: Why is black the color of discard?

Black made the best sense flavorwise of causing trauma to the brain. It’s vicious and kind of insidious. It’s also a bit more forward planning than red. You’re destroying things that later might hurt you. 

Also, blue, the other color that makes sense to be messing with the brain had counterspells. Mechanically, those two abilities overlap that you want them in different colors.