My experience is that those coatings, like "Back to Black" and others, really are only temporary. You used to be able to buy a product called "tire black" in a small paint-can. It was basically mineral spirits loaded with carbon black- think wood stain on steroids, jet black, and impossible to get out of anything you spilled it on. I'm sure it was an environmental abomination, but it actually worked decently on rubber and plastics. I even turned an old set of RWLs into blackwalls for one of my cars to play a copcar in a movie with it once.