It’s not that easy I think (and you had by far the best idea in this thread now).

Can’t make them red or orange, they’d be just turn signals.

Can’t make them green, that wouldn’t work for color blind people, and since you actually need the color for understanding what signal you get (unlike traffic lights) you actually have to make it work

And arguably you can’t really make them white, because you can’t see a white blinking light inside a headlight and couldn’t differentiate it from the back light. Same with light blue.

Which leaves darker shades of blue, which are really hard to see in daylight.