True so long as the others have red and blue lights. 
Some Motorway police have amber and red lights here in the UK. But i see a lot of cars and vand also using amber lights.
If they are turned off then i cannot see a problem with blue lights being there. The law states you can not have a blue flashing light that can be seen by others on your car.
Surely if the light is turned off then it isnt flashing? And even if you took the bulbs out of the light bar, to make it inanimate. Then it would not be able to be used, so there is no chance of it, whioch would make it no more illegal than a blue roof box or blue racing stripes
Lawrence
i read an article a while back about someone who bought a ecto-1 replica. They said just driving it back to their home after purchasing it, that they were stopped multiple times about the blue lightbars(i dont think they were written a ticket, but were given multiple warnings). So id have to say that unless your an emergency vehicle, amber would be the only color lightbar you could legally have. I seen pics of that ecto-1a replica and it looks like he has to put “out of service” covers over the lightbars to drive around town…damn…