Think RESALE. Many caps do oxidize and fade. It is NOT DUE TO NOT WAXING. It is due to poor foundation prep and paint. My 2015 Silverback 33rl fifth wheel came with mocha cap. Fade within 12 months. Professionally redone. 4 months later fade. I was at factory for other reasons. They offered choice of another moca cap OR oyster 2016 color. Matched my 2015 perfectly. I had the lighter cap installed.
Stay on the forums of both FR and Keystone with similar units you are considering. See what issues OR resolutions there are. Make an INFORMED CHOICE. If the resale market is for more streamlined looking units with fiberglass caps, bet you win at point if trade, all conditions equal. Caps are eye candy. Do what makes you feel good after you do your homework!
Focus your attention on hitches and tires. You will be ahead of the game!!