i used to own a black colored car and to be frank, the maintenance of the paintwork can kill. only way i figured to reduce and eliminate swirl, water, scratch marks etc was to send ur car for polishing at regular intervals or invest in a tough sealant to protect the entire paint job.
if u do it urself, it'll be quite impossible to keep up the work coz any minor scratch will magnify itself x100 against the black surface. having a good layer or wax to buffer against such scratches is a good idea but u'll have to wax ur car like almost every week..... dun go gym also can become body builder liao
