Which color is not permitted for stop lamps?

Stop lamps are critical safety features on vehicles, signaling to drivers behind when a vehicle is coming to a stop. The color of stop lamps is regulated to ensure uniformity and clarity on the road.

The use of blue as a color for stop lamps is not permitted because it could be confused with emergency vehicle lights. Emergency services typically use blue lights to signify their presence and, allowing blue stop lamps could lead to misunderstandings on the road, potentially compromising safety.

In contrast, red is universally recognized as the color for stop signals, while amber can be used in various situations to indicate caution or a warning but is not used for stop lamps. White is generally used for reverse lights and is not associated with stopping or braking. Therefore, blue is the only color among the choices that does not conform to the required standards for stop lamps.