Just a quick comment on this proceeded by "it would need to be measured.", and I believe it's likely that a white Oliver would be cooler than one that was painted or had a darker color...but... The term used to describe the absorbtion or radiation of energy is emissivity. The highest (perfect) absorber or radiator has an emissivity of 1.000.. A perfect reflector has an emissivity of 0.... Close to 40% of the sun's radiated energy is in the visible area of the spectrum, but nearly 50% of the energy is in the infrared. So, while the white is reflective to our eyes, most plastics and normal paints are very dark in the infrared. You'd like a lower emissivity number to both keep heating from the sun to be low and to lose less heat at night. The ideal direction would be something like highly polished aluminum (but not anodized). Shiny white and clean fiberglass is much easier to maintain, and probably much lower cost. And white of the same material would likely have a lower emissivity compared to a color - particularly a darker one.