Final answer:
Warning signs indicating upcoming hazards typically have black letters or symbols on a yellow background. This color combination is chosen for its high visibility and effectiveness in alerting drivers to potential dangers.
Step-by-step explanation:
The colors of warning signs indicating upcoming hazards have specific meanings to ensure safety and to alert drivers to potential dangers. Warning signs use the color yellow with black letters or symbols to convey information about hazards ahead.
Therefore, the correct answer to which colors of warning signs indicate upcoming hazards is black letters or symbols on a yellow background. This color combination is used because yellow is a primary color that is highly visible and therefore effective for cautionary purposes.
As per the National Fire Protection Agency (NFPA) 704 Hazard Identification System, other colors like red, blue, and white on safety signs represent different types of hazards but are not typically used for road warning signs about hazards.
For instance, a red diamond indicates a fire hazard, a blue diamond indicates a health hazard, and a white section signifies special hazards. Orange is another color used for construction and detour signs due to its high visibility and association with safety in various contexts.
Other colors, such as red, blue, and white, represent different hazard types but are not standard for road hazard warnings.