I dyed my hair black with temporary hair dye.....?

If you want the dye out now, you will need to seek professional help. It could be pricey and damaging to get the color stripped, but you will see instant results. Of course after they strip your hair, they have to dye it a base color. Up to you, but I think it would be best to just wash it out. You can use Prell or another let moisturizing shampoo that will probably get the color out faster.