Blue lights are illegal on non-emergency service vehicles. Red lights showing at the front of vehicles are also illegal, a black cab driver was prosecuted for having a miniature Christmas tree on his dashboard with red lights on it.
I had a look at the laws concerning vehicle lighting last month as I was wondering about the legality of putting fairly lights on your bike. As far as I remember you're not allowed to put blue lights on your vehicle as they are reserved for the emergency services. White lights shoudl not be visible from behind and red lights should not be visible from in front. You are allowed amber running lights along the side.
1. any means in or by which someone travels or something is carried or conveyed; a means of conveyance or transport: a motor vehicle; space vehicles.
2. a conveyance moving on wheels, runners, tracks, or the like, as a cart, sled, automobile, or tractor.