Nevada law does not specify nor restrict additional vehicle lighting equipment which would include neon under-glow. Therefore it’s concluded that in Nevada neon under-glow is not illegal, as long as you adhere to the following restrictions:
No amber flashing lights are permitted
All aftermarket lights visible from the rear of the car should be red
License plate illumination must be white
It is highly recommend avoiding blue and red colors on all aftermarket lights including underbody glow, as these colors are typically used on emergency vehicles.
Although not specifically required, to stay completely within the law you may want to consider using amber colored car under-glow in front and front sides of a vehicle, and red glow in the back and back sides.
There are no relevant NV laws which specifically restrict or prohibit installing car under-glow, meaning it's consider legal to use it while driving.
Nevada vehicle lighting laws
NRS 484D.145 – Colors of certain lamps, lights and reflectors
1. Front clearance lamps, identification lamps and those marker lamps and reflectors mounted on the front or on the side near the front of a vehicle must display or reflect an amber color.
2. Rear clearance lamps, identification lamps and those marker lamps and reflectors mounted on the rear or on the sides near the rear of a vehicle must display or reflect a red color.
3. All lighting devices and reflectors mounted on the rear of any vehicle must display or reflect a red color, except that:
(a) The stoplight or other signal device may be red, amber or yellow.
(b) The light illuminating the license plate must be white.
(c) The light emitted by a backup lamp must be white or amber.
(d)The tail lamp on a motorcycle may contain a blue insert as authorized in NRS 486.261.
NRS 484D.185 – Flashing amber warning light: Limitations on operation and display; permit to mount on certain vehicles; fee.
1. It is unlawful to operate or display a flashing amber warning light on a vehicle except when an unusual traffic hazard exists or as authorized in NRS 484B.748, 484B.757 or 484D.190. This subsection does not prohibit the use of amber lights in electric signals for making turns.
2. It is unlawful for any person to mount flashing amber warning lights permanently on a vehicle without a permit from the Nevada Highway Patrol.
NRS 484D.205 – Additional equipment for lighting.
1. Any motor vehicle may be equipped with not more than two side cowl or fender lamps which shall emit an amber or white light without glare.
2. Any motor vehicle may be equipped with not more than one running-board courtesy lamp on each side of the vehicle which shall emit a white or amber light without glare.
3. Any motor vehicle may be equipped with inside door-mounted red lamps or red reflectorizing devices or material visible to the rear of the vehicle when the doors are open.