When encountering other vessels in darkness or reduced visibility, what do visible white and green lights indicate?

During the night or in the event of reduced visibility, the ability to see what is happening around a vessel is greatly reduced. To avoid accidents vessels are mandated to use certain colors of light during this period. These light are called side lights and they are visible to other vessels that are approaching. The green light represent a vessel's right side while the white light represent the vessel's left side. Thus, visible white and green lights indicates that one is approaching another vessel head-on.