I over-darkened my piece but didn't worry too much, as I though I'd just lighten it up a bit using a product called "Color Oops". Well, after multiple attempts at this, the color has hardly changed! I've let it soak extra long, and nothing. I'm really surprised that it barely even lightened it, when it's supposed to actually completely take out the color. The parts of the piece I darkened should go back to blonde, but they're still dark brown. I know processed hair is said to retain dye longer than usual, but this is unbelievable.