Colored lights and their meanings vary form State to State.
In Missouri,
Blue lights are for volunteer firefighters.
Red lights are emergency vehicles (police, fire&ems)…SOME tow trucks can run red lights, but I don’t know how that works.
Green lights are used by Fire Dept’s to signify the command post.
Yellow lights are on large or slow moving equipment
Purple lights are on funeral procession vehicles.
The old Missouri laws stated that red=police; blue=fire; green=ambulance. But as time went on, ‘experts’ found that red was more visible during certain conditions, blue was more visible during other certain conditions…blah blah blah.
Because of those reports, emergency vehicles started running red/blue combinations to cover all the conditions and the law was ignored for the most part.
You may also notice yellow rotating lights on the rear end of fire trucks now. They started showing up in the early nineties because the National Fire Protection Agency said they should be on there.
As stated before, yellow lights are more for attention, so you don’t run into them when they are moving slow or making weird turns while plowing a parking lot.
The purple lights are a more recent addition to the Missouri laws for funerals.
As I said before, each state is different and in some states, each county can be different. If you are a volunteer firefighter with blue lights on your vehicle and you travel to a state that use them on police cars, be prepared to get pulled over. They will make you either take it down or cover it up.