What color lights are used as sidelights on a vessel?

Sidelights on a vessel are used to indicate the vessel's presence and direction of travel to other boats. The correct colors for sidelights are red on the port (left) side and green on the starboard (right) side. This color coding is universally recognized in maritime navigation, helping to avoid collisions by indicating which direction the vessel is facing. For instance, when a vessel is approaching, if you see red, it means you are looking at the port side, and if you see green, you are viewing the starboard side.

This system of colored lights is critical for maintaining safety on the water during both day and night. The other choices do not align with the international maritime standards for sidelights, which is why they are not correct. Red and yellow, green and yellow, or white and red do not provide the necessary indication of a vessel's orientation and direction that red and green lights do.