Humans use lights to signal as well as to illuminate, using colored stop-and-go lights at intersections, on landing strips, and on exit doors. Colors are also symbolic, from the black robes of the judiciary to the white robes worn by nuns. Thus when sightings include reports of colored lights on ships, or even ships of various colors, they assume this to be in part a signaling process. It is not. Human society, being a 3rd Density society, cannot prevent interaction between individuals or groups, and thus signals and signs are valued for the assist they give to structure. Red light means stop, flashing light means impending action, neon light means the establishment is open, and direction can be indicated by following the moving arrow. Lights, and in particular colored lights, are a communication vehicle in human society.
But should humans travel to another world, a red stop light would not carry the same meaning, and with the advanced technology used by visitors, signaling each other with colored lights is not necessary. All ships, from all groups, are aware of each other due to computer coordination of visitors from the Council of Worlds. We are aware of each other, sight unseen. Then why different landing lights on our ships or different colored beams of light or different colors in examining rooms? It's commonly known that lights in different spectrums illuminate different aspects of an object by causing a reaction in the bathed object, and that some color spectrums cannot be seen by certain life forms. Horses and dogs, for instance, are color blind. Thus, our ships use many more lights than humans are aware of, assuming as they do that we zip about in the darkness when in fact they simply can't see the lights we are using. And when different colored lights are seen, this is not a deliberate use of color but a deliberate functional use of different wave lengths. The color is incidental and irrelevant.