Federal DOT laws are for all states. Period. Every vehicle brought into US must meet Federal DOT lighting laws. Look em up. Any introduction of another color in itself is a violation of federal law and can be enforced. I have explained the reasoning before but it is easy enough to look up on google.
If you have legal reason you can have these colors. They do Vary by state but you will need reason to display them or risk a ticket.
The Colors Used in the United States
Now, here is a quick guide that you can use to recognize the meaning of the color of light used. Remember that these colors differ in each country, and the following are applicable for emergency vehicles in the United States:
1. Amber or Yellow: This color designates utility vehicles which could be moving slower than usual. Amber lights can be seen in tow and construction trucks, security patrol cars, funeral escorts or vehicles used to remove snow.
2. Blue: Blue is typically used on law enforcement vehicles – but they are also used in tow trucks and in the vehicles of volunteer firefighters in other states.
3. Green: Depending on the state where it is used, a green light designates a fire chief's car, a mobile command post, a volunteer firefighter's truck or private security guards.
4. Purple: There are some states where purple lights are used to denote a funeral vehicle.
5. Red: This is probably the most familiar color, which is used to denote an emergency.
6. White: A flashing white light can be used by school buses or fueling tankers.
I think in Ohio Green is also Coroner's car or color. All I do know is it pisses LEO
's off when you use colrs you are not authorized to.