Blue neon

Probably not.

Here is what I believe to be the relevant CA Vehicle Code Section:

25102. In addition to the lamps otherwise permitted by this
chapter, any motor vehicle may be equipped with lamps on the sides
thereof, visible from the side of the vehicle but not from the front
or rear thereof, which lamps, together with mountings or receptacles,
shall be set into depressions or recesses in the body of the vehicle
and shall not protrude beyond or outside the body of the vehicle.
The light source in each of the lamps shall not exceed two
candlepower and shall emit diffused light of any color, except that
the color red is permitted only on authorized emergency vehicles.

 

In Indiana, Blue neons violates the Indiana Blue Light law...Blue Lights are authorized on vehicles belonging to Firefighters and authorized emergency vehicles...ie Police vehicles. No Blue light may be showing in any direction except in the above aforementioned. police run red and blue, firefighters run blue...emergency medical techs run green, and fire trucks, ambulances run red with combos of white.

 

So i can as long as the light source isn't seen.. ok.. i'm sure neon lights are not considered too bright

 

I don't have the patience to go through every CA Vehicle Code section regarding lights. You can access it at this website: CALIFORNIA VEHICLE CODE.

The lighting equipment is covered in sections 24250 through 26106.