Dark Temper deals 2 damage to target creature. If you control a black permanent, destroy the creature instead.
Dark Temper has a self-replacement effect, which applies before other prevention or replacement effects would. If you control a black permanent as Dark Temper resolves, it doesn’t deal damage at all (so damage prevention or redirection effects would have no effect); it simply destroys the targeted creature.
This checks the colors of permanents you control as it resolves.