Even the blue glowing lights inside your grill are a huge issue if you get caught. I did a lot of investigating because I was considering red lights. Red halos look really cool, but that vehicle was from another country.
Here are some examples from the Internet:
South Dakota:
"Any motor vehicle operated by a member of an organized fire department or organized search and rescue unit may be equipped with flashing blue lights displayed to the front or a blue rotating beacon light or strobe light or both to be visible 360 degrees. This provision does not relieve the driver of such a vehicle from the duty to drive with due regard for the safety of all persons using the street nor does it protect the driver of any such vehicle from the consequence of a reckless disregard of the safety of others.
No person may use a light described in this section except a fireman or search and rescue unit member while actually en route to the scene of a fire or other emergency requiring his services as a fireman or search and rescue unit member, who has been authorized in writing to so use a blue light. Such authorization shall be given by the chief of the fire department or coordinator of the search and rescue unit only to members of the department who are in good standing.
A violation of this section is a Class 2 misdemeanor."
"I would stop a car with extra lights hidden in the grille. If they were blue then that would be a severe ticket. Blue is the color for police vehicles and I want the public to be 100% sure that when they see blue lights it is a real cop car -for their safety and mine."
Tennessee:
"With that said, in TN no vehicle can have any type of strobes, wig wags, or flashing lights (no matter the color) unless authorized LEO, FF, or rescue squad member (with permission from agency head). There are certain colors for work vehicles (TDOT, tow trucks, etc). Under TN state law, it doesn't specify non-flashing lights and that's how some get away with it, but in metro Nashville (Davidson Co.) no vehicles can have blue lights at all, whether flashing or non-flashing. This includes forward facing neon, grill lights, or even the little steady blue lights on windshield wiper sprayers."
Florida:
"In Florida you can go to jail just for having them installed on your vehicle, whether in use or not...
843.081 Prohibited use of certain lights; penalty.--
(1) The Legislature finds and declares that Florida's citizens are vulnerable to becoming the victims of criminal acts through the illegal use of blue lights by the criminal elements. It is the intent of the Legislature to reduce this vulnerability to injury and loss of life and property by prohibiting the use of certain blue lights by any person other than an authorized law enforcement officer.
(2) It is unlawful for a person to use in or on any non governmentally owned vehicle or vessel any flashing or rotating blue light unless such person is a law enforcement officer employed by a federal, state, county, or city law enforcement agency or is a person appointed by the Governor pursuant to chapter 354.
(3) The provisions of this section shall not apply to salespersons, service representatives, or other employees of businesses licensed to sell or repair law enforcement equipment.
(4) For the purposes of this section, the term "flashing or rotating blue light" includes all forms of lights which display a blue light source or which were designed with the intent of displaying a blue light source whether or not such light is actually in use.
(5) Any person who violates any of the provisions of this section commits a misdemeanor of the first degree, punishable as provided in s. 775.082 or s. 775.083."