Laws regarding red/blue lights vary widely from state to state. I'm just speaking "technically" since what you get away with depends greatly on your actions and the mood/disposition of the observing officer.
The company I work for is a distributor for emergency lighting, I'm regularly in possession of red/blue lighting and we have two fully outfitted demonstrator vehicles which in our case is excluded from the statutes below. But it's pretty plain here, no blue lighting on a public highway driven vehicle. You want to outfit your mower/tractor/anything else and only drive it on your own property go for it. Just don't operate it on public access. I've seen ricers be pulled for the little lighted windshield washer nozzles that were blue. LOL !!
North Carolina General Statutes 20-130-1c
It is unlawful for any person to possess a blue light or to install, activate, or operate a blue light in or on any vehicle in this State, except for a publicly owned vehicle used for law enforcement purposes or any other vehicle when used by law enforcement officers in the performance of their official duties. As used in this subsection, unless the context requires otherwise, "blue light" means any blue light installed on a vehicle after initial manufacture of the vehicle; or an operable blue light which:
(1) Is not (i) being installed on, held in inventory for the purpose of being installed on, or held in inventory for the purpose of sale for installation on a vehicle on which it may be lawfully operated or (ii) installed on a vehicle which is used solely for the purpose of demonstrating the blue light for sale to law enforcement personnel;
(1a) Is designed for use by an emergency vehicle, or is similar in appearance to a blue light designed for use by an emergency vehicle; and
(2) Can be operated by use of the vehicle's battery, the vehicle's electrical system, or a dry cell battery.