Which color combination indicates a vessel that is not under command?

The color combination that indicates a vessel that is not under command is red/red. This signal is used to ensure that other vessels are aware that the one displaying this configuration is unable to maneuver as required by the rules of navigation.

A vessel not under command may be unable to navigate due to issues like mechanical failure or other emergencies, and the red/red lights, displayed at night or in reduced visibility, serve as a clear signal to other vessels. The red color is universally recognized in maritime navigation as indicating a danger or a vessel that is in distress or restricted in its ability to maneuver.

In contrast, each of the other combinations signifies different scenarios. For example, the red/white combination typically indicates a vessel that is constrained by its draft, while green/white is used for vessels engaged in fishing or other navigation activities that may involve restrictions. All white lights are typically seen on vessels at anchor or other situations that are not representative of a vessel not under command. Understanding these signals is critical for safe navigation and avoiding collisions on the water.