Excellent question. I have wondered the same thing. I observed some unconventional aircraft which had the conventional green-red navigation lights, and some unconventional aircraft with very diverse lighting schemes which were clearly not conventional. I saw craft turn on and off certain lights which, at night completely change the appearance of the craft. I occasionally saw aircraft stop and hover in the sky, and for several minutes would emit very bright intense colors of red, green, blue, purple, yellow etc. For some reason I got the sense that those lighting displays were a form of communication.