I've had 'white streaks' on other rv's we've owned, due to the rubber roof material becoming oxidized over time. Used rubbing compound and a lot of elbow grease to remove the streaks from the gel coat on the side of the rig. Our Beaver, with the fiberglass roof doesn't have any 'white streaks', the only streaks come from rain or condensation (Ore /Wash coast in AM) working its way down the sides and carrying dust with it. Our '05 Beaver does not have a 'drip rail' on the side as my previous 5th wheel and TT's have had. As for roof color, we know that white reflects all light, darker colors have less reflectivity but I don't know if that affects UV absorption.
I'm a big believer in the 'Wash Wax All' stuff. The long handled wash mop gives my upper body a workout as I use it to clean a small area using the wet side of the mop, then quickly use the other 'dry' side of the mop to dry and polish the area just cleaned. Boy, the rig sure shines in the afternoon as I enjoy a beer!