Well, whether it makes a difference in practice depends on questions like: What fraction of sunlight's energy is delivered in the visible spectrum that the whit

Well, whether it makes a difference in practice depends on questions like: What fraction of sunlight's energy is delivered in the visible spectrum that the white paint would reflect? (Are there any significant differences in absorption of infrared or UV that would counteract it?) How much total power does that integrate to over the area of the car? At what rate does the heated exterior of the car conduct heat into the interior? Etc. I don't know these quantities myself. As I wrote the above message, it seemed possible that the effect could turn out to be very small and not worth bothering about; I vaguely remembered reading that it might be a few degrees. Well, if we google a bit: "We took two nearly identical vehicles, one white and one black, and let them bake in the hot Georgia summer sun. When we measured the interior temperature after a few hours, ... The black car’s cabin measured a scorching 130 degrees Fahrenheit, while the white car’s interior registered only 113 degrees." https://www.autotrader.com/car-video/car-color-test-are-black-cars-really-hotter-sun-video-242940 https://www.autotrader.com/car-video/car-color-test-are-blac... Ok, that is substantial.