My original '69 RR Air Grabbers weren't painted black; they were a dark charcoal color with the fiberglass strands clearly visible. I'd say the color came from the resin that was used.
I restored one of them by scuffing it and spraying a satin clear over it, which rejuvenated the faded color & hid some scuffs.
That car took 1st Place Restored at the Nats a few years back, so I guess it was good enough for some pretty picky folks.