I thought white was already the best possible from Elon's point of view...

Hmmm, closest thing I’ve seen is clear vs “smoky glass” using liquid crystal technology. $$$ Or how about OLEDs, conformable digital “screens” designed to fit any (e.g., automotive) shape. $$$$$ In that case not just any color but any fixed or moving image— imagine the traffic issues! Back to black or white, how about using an electrically stimulated thin-film coating… $$