What color lights should be visible at the rear of the trailer?

The rear lights of a trailer must be red, which serves important safety functions on the road. Red lights are universally recognized as a warning signal indicating that a vehicle is present and can help prevent accidents by making the trailer more visible to drivers approaching from the rear, particularly in low-light conditions or bad weather. Furthermore, federal regulations and most state laws specify that the rear of any vehicle, including trailers, must display red lights to comply with safety standards.

Other colors such as blue and green are typically associated with specific warnings or emergency vehicles, and yellow lights generally indicate caution or slower-moving vehicles. Therefore, they do not meet the legal requirements for the rear lighting of trailers.