You'll need a deep saucepan, dye, acetone, gloves and a good dust mask. Not the paper ones. I recommend you buy one with the replaceable filters.
So you fill a deep saucepan with 3/4 of water
Add 3 cap fulls of dye (you can only dye plastic darker! You can't dye red plastic yellow.)
Add a cap (and I mean the bottle cap BTW) of acetone to the dye
Keep an eye on the hotplate and bring the dye to the boil. Don't let it boil over turn off the hot plate.
Add the plastic to be dyed. Leave in the pan stir often and remove when the desired colour has been reached.
Rinse parts under a running tap of cold water.