I use wet and black on mine.
Before i actually started driving the car is wasnt washed very often so the black plastic at the back of the car and areas where dirt and water would hit more were a bit lighter than the rest.
i used wet and black about 1/2 times a week to build it up and now I can leave it for near 2 weeks before the really black look fades so i do it again. Works a treat.
The only downside is that it doesn't work on tyres as well as it should but that is what son of a gun is for
