How do you remove hair dye?

Right now my hair is white and I need to dye it for a SINGLE day, but I really like the color it is now. Pi-moo tried "Color Ops" but all it did was smell really bad. :P The dye I think I'll be using is "Manic Panic", I know it's only semi-permanent but I'd like to return to white as soon as I can after wards.