In the US, to be convicted of a crime, it has to be proven beyond a reasonable doubt that you intended to commit the crime.
Simply flashing red or blue light does not prove intent of impersonating a LEO or Firefighter.
You might get away with that sometimes, but ignorance of the law won't excuse you from it. It's too easy to just say "duh- I didn't know that" ...that won't fly LOL.
You can accidently run a red light unintentionally...you still ran the light and can get a ticket. Someone does have to witness you breaking a law in some cases a cop specifically has to witness it. Too easy to argue it didn't happen, or "I didn't do that, someone else did"
You can accidently run someone over, yep you ran them over. It's manslaughter. Intensions don't matter.
Intentions can play a part in how hard the court tries to press you. Accidental manslaughter is one situation.
A lot of states/cities have specific laws against 'blue lights' flashing or not. Others might not. Some apply them to any vehicle on public roads. Gas/electric motor driven, steam powered, self-powered, gravity or wind it doesn't matter. If it's on the road then they have to follow the laws/rules of the road.
Pedestrians are a different thing. I haven't seen nor heard anyone getting into trouble walking around with flashing red/blue lights on. Other than festivals, fairs, I can't think of any time I've seen a pedestrian wearing those sorts of lights in public. I personally wouldn't wear those in public but that's me.
I haven't found any laws prohibiting such activity.
I'm just thinking out loud, if it becomes a common thing a fad of sorts, then laws might be made or existing ones enforced to eliminate any confusion and for safety.