In most states, neons are illegal for street use... period, it doesn't matter what color they are.
If you have them, put them on a switch, it's okay to have 'em on when your parked, or at private events, or when the car is being shown, but if you are driving, and have neons lit, prepare to get a ticket.
Most states ban them because they are a distraction to other drivers on the road. I saw a kid in a honda and another in a truck, they both had neons, I shook my head, and about 30 secs later, they were BOTH pulled over by the cops.
The same rule of thumb holds true for LED windshield nozzles, city lights and interior neons (you're not supposed to have any internal lighting on when driving excepth for gagues consoles & shift lights. even the dome light being on while moving is illegal if a cop sees it in most states)
Your best bet is to go to your local DMV, and pick up a copy of your local motor vehicle code; it should be freely available.
For example, in Illinois:
all forward facing lights should be white to amber in color.
Brake lights must be red, rear turn indicators must be red to amber in color.
one set of headlights, and one set of auxiliary lights are the max allowed, all other auxilliary lamps must be disabled on the street.
HIDs are legal, so long as they conform to the pre-set laws regarding headlamps (ie: amber to hyper white in color, if they're super blue, they're not legal.)
this is just a sampling, the laws get into more detail. if you don't follow the local laws in your area, every cruise is a roll of the dice.