The standing joke in the marine industry says that a boat can be any colour, as long as it is white.
That holds true with RVs too. Colour simply does not hold up to the ravages of the sun. Add this to manufacturers who, in an effort to minimise weight & costs, spray very thin gel coats into molds. A new unit may sit, with no maintenance, no wax, in a lot for a year before it is sold. The dealer uses something cheap & easy before sending it out the door then the owner either does not maintain it or also uses something cheap & easy which typically does not last very long before it is chalking again.
The darker it is, the faster it will chalk.