Nissan Motor Co. said it has developed a new type of paint that significantly reduces the temperature inside vehicles parked in direct sunlight.
The surface of a car coated with the innovative material remains up to 12 degrees cooler than that of a vehicle with standard paint, tests showed.
The company said the coating material can help rein in the temperature rise not only on the car’s body but also in the vehicle when exposed to direct sunlight.
OK I’ll link the danish test, this test is done with 2 cars that are identical, except for the color of the paint:
https://livsstil.tv2.dk/2018-05-24-bliver-en-sort-bil-varmere-i-solen-end-en-hvid-tv-2-har-lavet-testen
Translation:
The conclusion is that the black car does not heat up noticeably more in the sun than the white.
So it does a little bit that you can measure, but not enough to really make a difference.
According to Christian Bahl senior researcher at DTU energy, that is because the cars are heated through the windows.
(DTU is a well recognized institution for scientific research in Denmark.)
Maybe the fact that the experiment was done when outside were only 20-22 degrees made the difference less noticeable? Otherwise I can’t explain why all the other tests I’ve found said the difference was 5-10+ degrees.