What is the primary color used for warning signs like the HILL sign?

The primary color used for warning signs, such as the HILL sign, is yellow. This color is specifically chosen for its visibility and high contrast, making it easily recognizable to drivers. Yellow warning signs are designed to alert motorists to potential hazards or changes in road conditions that require caution. Signs like the HILL sign indicate that there is a steep incline or decline ahead, prompting drivers to adjust their speed and approach with vigilance to ensure safety.

Yellow's significance in traffic signage comes from its association with warning and caution, differentiating it from other colors used for regulatory or informational signs. Other colors have specific functions: for instance, white typically denotes regulatory signs, blue is usually associated with informational signs, and orange is used for construction and temporary conditions. Thus, the use of yellow for warning signs is crucial for effective communication with drivers and maintaining road safety.