My S2 & S4 both run black losi wheels dyed with dylon, best place i have found to buy it online is
http://www.chaffinch.com/ and goto Dylon Multi Purpose Dye. Also dyed some parts Tangerine

its important to add salt to your dye as this helps the dye bite into the plastic. And for wheels use two tubs of the dye, and use a old saucepan as it really is not fit for food after