I clean it with a sponge every time I wash it but I get "stains" or maybe they are large water marks.
I bought some back to black (which works great on the bumpers, door handles, door gaurds and front fairing(?) where the wipers are) I used it on the plastic part of the step rails and it worked but didn't last too long (becuase my son steps on them to get up and in.
I had an old bottle of Armour All and used that on the plastic and also the metal and it works pretty good.

Just my 2 cents