Here is something interesting i found:

In the UK, police cars use blue lights with additional white lights at the front and red lights at the rear to help other road users determine direction of travel. The rear red lights can be switched on and off separately from blue lights to indicate caution.

I thought we figured out that red, and red shifted light can cause aggressive moods and reactions to some senative people so I was expecting to find that they stopped using them, but i have not seen this anywhere that I have researched so it is probably just a me thing, and not supported by evidence.