You will need: Vegetable dye (Manic Panic, Directions, Special Effects etc), your usual conditioner or hair treatment, mixing bowl and mixing brush and hair dying gloves.
This method ONLY WORKS with veggie dyes - Special Effects, Manic Panic, Stargazer, Directions, Crazy Colours etc. 'Normal' dyes don't take as well when mixed with conditioner and wont store, either. Veggie dyes are fab because you can mix your own shades, dilute them and they keep for aaaaaaaages (I've got one from 5 years ago!)
Do you use this method? If you could have any hair colour at all - what would it be?