In my parents' car, the screen doesn't exactly have high dynamic range, and for some reason Google Maps colors are white on white, impossible to tell where the streets are looking at the screen during the day.

That's Google design these days. White on light white on sightly darker white.

Apparently it's modern and people have thought about it. I guess those people wear sunglasses all day.

I keep telling this at my Google maps when I use it as satnav in my car. I'm trying to count which right it is, but I don't see the side streets as they are white with a light grey border on off white. Infuriating. Give me my neon green, purple and black.

These situations are not the same btw. Not sure if you know, but this style was added as an option in the layers menu. You can use whatever style you like!

The reason they use such light, poor contrast colors is that the map is used as a background for things like business ads, the blue navigation line, etc. Yes in the process, it becomes useless as an actual map for looking at.