When I was shopping for my current unit, there was a gray unit that I seriously considered until I put an IR gun on it. I tested two units from the same manufacturer, right next to each other, the gray unit and a white one. Difference in outside temp was shocking, and even on a sunny December morning at 10am, inside temp for the gray unit was already 6 degrees higher.
From an investigation of house paint colors I did a few yrs ago, I believe the cream color RVs will not be near as hot as gray. But I haven't done a comparison of all the different RV colors. A lot also depends on roof color as well. I'll stick with boring white.