I spoke to a CA Highway Patrol Officer and asked your question.
Neon lights are illegal on the machine. Even the ones that surround the license plates.
I think the officer said to look at the vehicle code book which has the requirements for lights. It probably says that stop lights must be red, turn signals must be red or amber, back up lights white, license plate lights white...
Even those blue lights that the young kids install on their hoods are illegal. If the CHP sees them, they can pull you over for a fix it ticket...
I guess the police don't want to see a Truck Conversion barrelling down the freeway at 65mph with a look like it's floating down the road???
Don't know what's wrong with that. I think it would look cool and there's a lot of square footage that would be available for that "floating look."