Black is the hardest to keep clean, but equally gives the best results when detailing. For most cars I would recommend as little polishing as possible, especially on something like an RS500. My advice would be to get the paintwork cleaned and prep's ready for some good long lasting sealant. Either by claying the car or by using a decent paint cleaner. A nice finishing polish or like previously stated, Poor Boys Black hole works well on black cars. My recommendation for a sealant would be Chemical Guys Jetseal 109, it gives excellent results and lasts well. Follow this up with a decent lasting wax like one of the Collinites and your all done for around 6 months. Just wash and dry

Heres some black cars i have done with Jetseal.