What vessels may show an all-around red over an all-around green light?

The appropriate context for understanding why a sailing vessel underway may display an all-around red over an all-around green light lies in the application of the International Regulations for Preventing Collisions at Sea (COLREGs). According to the COLREGs, sailing vessels that are under sail but not using an engine while underway exhibit these lights to indicate their status and to ensure visibility to other vessels.

The all-around red light signifies that the vessel is either at anchor or has restricted maneuvers, depending on its specific operation. The all-around green light serves to indicate that the vessel is engaged in sailing activities and is navigating under sail alone. By displaying both lights, a sailing vessel underway communicates its active operation while ensuring that its status is clear to other nearby vessels, preventing potential collisions.

This specific combination of lights distinguishes the sailing vessel's operation from other types of vessels, such as power-driven or fishing vessels, which have different lighting requirements to indicate their navigation methods or fishing activities. The other options would not correctly utilize this light configuration under the defined scenarios in the COLREGs.