What color is a diver-down flag?

The diver-down flag is recognized internationally as a symbol to indicate that divers are in the water and that boats should use caution when navigating through that area. The flag is red with a white diagonal stripe extending from the upper fly to the lower hoist side. This distinctive coloring is designed to be conspicuous and catch the attention of boaters, ensuring the safety of divers by alerting them to the presence of divers below. Therefore, red and white is the correct answer, as it adheres to established maritime safety regulations regarding diver warnings.