Lights must not rotate, oscillate, or flash, but state law does not prohibit the use of colored neon lights under your car as long as they do not interfere or blind other drivers. Ohio Revised Code, section 4513.17 prohibits flashing lights on motor vehicles with the exception of emergency vehicles, turn signals, and hazard flashers.
Colored lights, such as neon lights around a license plate are not illegal so long as a separate white light is the PRIMARY illumination for the plate. If the neon light is the only source of illumination for the plate, or it changes the visible colors of the plate, the neon lights could be illegal. State law requires a white light to illuminate the rear license plate.