Necroing this to say the type of white pigment is important:
IIRC
This guy, who does the research, then makes it DIY, found that Calcium Carbonate (Whitewash) pigment was best at reflecting the IR light that heated surfaces and made paint:
He provides links to the science in the comments.
That's not going to work on dashboards reflecting in the windscreen and disrupting your view of the road, so thx for the window film info.