I remember when I lived in MD, it wasn't. Back then, the GTS smoke covers were the trend, and SERO citations were issued routinely with a $45 fine.
This is the closest I could find:
2 - ILLEGALLY COLORED LIGHTS - Another violation which seems to be in abundance lately is vehicles with lights or lenses
which are in violation of the Maryland Vehicle Law. Officers are routinely stopping vehicles with Blue, Green and Purple
lights added to/or mounted in lieu of, the vehicle's original lights. (The small "laser" lights mounted to the hood are the most
common violation.) We're also finding many people who have removed the Red Lenses and Reflectors from the tail lights
of their cars, and installed CLEAR lenses instead. (Clear lenses are legal only if the bulbs themselves are still located
behind RED plastic, and the required minimum amount of RED Reflecting Material is installed in the clear lenses.)
The Maryland Vehicle Law clearly states the colors which are required on the front, back and sides of vehicles used on
public highways, and these laws are in conformance with the Federal Safety Standards for Motor Vehicles
manufactured in the United States. Changing or altering these required items subjects the vehicle operator to a
Moving Vehicle Traffic Citation, (usually $40-50) and/or a Safety Equipment Repair Order. Again, be forwarned that just because a product is sold in a retail store like Trak Auto, Pep Boys, etc., that does not mean
that it is legal to use it. Most "after-market" vehicle products have a small disclaimer listed somewhere on the box or
package, which reads: "NOT FOR HIGHWAY USE," or "CHECK LOCAL LAWS BEFORE USING THIS PRODUCT."
The manufacturers of these products do this to place the responsibility for using their merchandise on YOU.
Even if a disclaimer is not listed on a particular item, the responsibility is still on the owner or operator of the vehicle
to make sure that it complies with the law when used on the public highways of the state.
Additionally, Maryland law requires that any after market device sold must be approved by the Administrator of
the Department of Motor Vehicles, before it can be installed on a vehicle. The small "Laser" Lights mounted on the hood,
Neon Tubes mounted under the vehicle which give a "glowing" effect, and many of these other "auto parts store" items
have NOT been approved for use on vehicles in Maryland.
WHEN IN DOUBT ABOUT A PARTICULAR AFTER-MARKET ITEM, CONTACT THE MARYLAND STATE POLICE -
AUTOMOTIVE SAFETY ENFORCEMENT DIVISION AT (410) 424-3787 FOR AN OFFICIAL RULING.
SAVE YOURSELF UNECESSARY FINES, POINTS OR IMPOUNDMENT OF YOUR VEHICLE!