What color indicates a warning sign?

The correct choice identifies that yellow, and in some cases green, is used to indicate warning signs. Warning signs are crucial for alerting drivers to potential hazards, changes in road conditions, or other developments that may require caution. Yellow is the standard color for caution, as it stands out and catches the attention of drivers, prompting them to be vigilant.

Green, while primarily associated with guide signs and information regarding directional routes, is sometimes used in conjunction with yellow in specific contexts, particularly in certain states or situations where clear communication of caution is necessary.

The other options represent different sign categories: red is used for regulatory signs, indicating stop or prohibitive actions; orange is used for construction signs, warning drivers of work zones; and blue generally indicates informational signs or services. Each color serves a specific purpose in road signage, and understanding these distinctions helps ensure safety and compliance on the road.