What lights are shown by a pilot vessel when not on pilotage duty?

When a pilot vessel is not engaged in pilotage duty, it is required to display the lights prescribed for vessels of its length. This means that the vessel must follow the standard navigation lights as stipulated by the COLREGs for its specific size. This is important for ensuring that the vessel is properly identified by other mariners, contributing to maritime safety and communication.

This requirement helps prevent confusion when such vessels are present in navigable waters, particularly when they are not actively serving their primary function of transporting pilots. By adhering to the prescribed lighting configurations, the pilot vessel maintains visibility and conformance to regulations, ensuring that it can operate safely alongside other commercial and recreational vessels.

In contrast, other answer choices reference specific light colors or suggest the absence of lights, which do not align with the operational standards set for vessels in general navigation. Displaying incorrect lights or no lights at all could lead to misunderstandings about the vessel's status and intentions, potentially compromising safety on the water.