Which of the following is a violation in vehicle illumination?

Using colored taillamps is a violation in vehicle illumination regulations because tail lights are required to emit red light to indicate when a vehicle is stopping or slowing down. The purpose of standardized lighting colors is to ensure clarity and consistency on the road for safety reasons. When vehicles use colored taillamps that deviate from this standard, it can confuse other drivers and lead to unsafe conditions.

In contrast, other choices relate to vehicle lighting but do not inherently violate safety or regulatory standards. For instance, using multiple headlamps can be allowed as long as they comply with the specified brightness and placement regulations. Malfunctioning turn signals indicate a maintenance issue but do not categorically constitute a violation of illumination practices; however, it can lead to unsafe driving circumstances if not addressed. Similarly, not having a backup light may present an operational challenge but falls short of being a direct violation regarding illumination standards.