I did it it with them on the car. theres a thread about it somewhere. i just cleaned the bumpers with sugar soap, then thin coat of primer to make em whiteish.. then 3 layers of thinly applyed colour. when it looks how you want stop adding layers then put a thin coat of laquer on it to make it a bit shiny. i had mine like that for about 8 months and nothing flaked off or anything!