What color is a signaling device mounted on the rear of a vehicle NOT permitted to be?

A signaling device mounted on the rear of a vehicle is not permitted to be white because white lights are typically reserved for specific uses, such as headlights or reverse lights. The purpose of signaling devices, such as brake lights or turn signals, is to communicate the vehicle's intentions to other road users. When it comes to rear-facing lights, red is commonly used for brake lights, amber is used for turn signals, and blue is reserved for law enforcement vehicles.

The use of white lights on the rear can create confusion among other drivers, as the standard color conventions for signaling do not include white for these purposes. Keeping these conventions consistent helps ensure that drivers can quickly and accurately interpret the signals being sent by other vehicles, which is crucial for safety on the roads.