When operating under sail at night which light should be used?

When operating under sail at night, vessels are required to display a red and a green sidelights, as well as a white stern light. The red light indicates the port side, while the green light represents the starboard side. Additionally, a white masthead light may be shown if the vessel is over 20 meters in length. These lights help ensure visibility to other vessels and indicate the sailboat's direction and status.