What color must the lighting device on the rear of a slow moving vehicle be if not provided?

The lighting device on the rear of a slow-moving vehicle must be red if not otherwise provided. This is because red is universally recognized as a color that signifies caution and alerts other drivers to the presence of a slower vehicle. Slow-moving vehicles, which typically operate at speeds less than 25 miles per hour, can create hazards on the road, especially when they are traveling in areas where other vehicles are moving faster.

The use of red for the rear lighting helps in ensuring that these vehicles are visible from behind, allowing other drivers to adjust their speed and position appropriately for safety. Additionally, the standards governing the visibility of slow-moving vehicles dictate that red must be used specifically for this purpose to convey the appropriate warning to other road users.

In contrast, the other colors mentioned are typically associated with different functions: white lights are generally used for forward illumination, green is not commonly utilized in traffic warnings, and yellow may indicate caution in some contexts but does not specifically denote the same level of alert that red does for slow-moving vehicles. Therefore, the choice of red is essential for enhancing safety and awareness on the roads.