What color are the lights required on the back of a large truck or trailer?

The correct answer is that the lights required on the back of a large truck or trailer are red. This is because red lights are universally used for tail lights and brake lights on vehicles, as they are easily recognizable and signify the presence of a vehicle to others on the road, especially in low visibility conditions. This is crucial for safety, as it allows following drivers to see when the vehicle is slowing down or stopping.

In contrast, the other colors have specific functions or uses elsewhere on vehicles or for signaling. White lights are typically used for headlights and reverse lights, while amber lights are often used for turn signals or hazard lights. Blue lights are generally designated for law enforcement vehicles and are not a standard requirement for large trucks or trailers.