Suggest using the interior dye system from Ames. The first step is a concentrated cleaner mixed in water to degrease the parts, 2nd is an adhesion promoter that dries a bit tacky, 3rd is a vinyl dye spray.

I just converted some black interior parts to parchment last weekend with success, despite having to add Step 2a to apply a lot of an off white dye, so your conversion from one shade of black to another should be much easier. 1/2 of my parts were the hard plastic trim around the rear window, the other 1/2 were the soft vinyl covered pinch weld covers at the rear door jam.