Sem is really good stuff. They have vinyl prep and good plastic paints and many other products. Mineral spirets works well at removing paints/dyes. It works slow but won't harm the plastic.
Good idea with the mineral spirits. Your local auto paint supply store should have a few non-material harming chemicals to try, too. You can always try blowing it off with compressed air also, as this won't harm the texture of the plastic, unless you let go and it launches across the driveway...lol.
What are you going for on the color choices? If something straight up like black, white, or some of the factory choices, then, as has been suggested to you SEM is great choice in a spray bomb. But if you want something a little more custom Bulldog adhesion promoter will help just about any paint stick to 'em after the proper prep work.