What must be used during the day and night for prescribed colors?

Flags and lights are essential tools used to convey prescribed colors for communication during both day and night operations. The use of flags during the day allows for visibility and clear communication of specific instructions or warnings, while lights serve the same purpose in low-light conditions or at night. This dual functionality ensures that important signals are effectively communicated regardless of the time of day, promoting safety and operational efficiency.

The other options focus on different means of communication that may not be consistently effective in both light conditions. For example, signals and signs might be more variable in visibility based on their design and placement, and banners and indicators might not provide the same immediate recognition needed for urgent situations. Similarly, markers and displays may not serve the necessary requirements for clear and standardized signaling needed both during the day and at night.