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Nissan develops paint that keeps cars cool in summer heat
(www.asahi.com)
This is a most excellent place for technology news and articles.
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.