A couple of years back I was doing a "redeye" from LA to Miami and about halfway across the US, shortly before sunrise I noticed a bright light on the horizon in the eastern sky that appeared to be white but would change colors to blue or red, it also appeared to move and "bobble" slightly.
Our first reaction was that it was an aircraft approaching us head on at an altitude close to ours with it's landing lights on. A quick check of our TCAS followed by a query to an otherwise silent ATC showed no other aircraft in our vicinity.
After several minutes the light did not get any closer, nor did it go away, but a carefull check of it's assencion relative to the horizon showed that it was slowly rising. Clearly what we were seeing was a bright star or planet, the changes in color were probably caused by refraction in the atmosphere and the motion we witnessed was most likely an illusion caused by movements of our own eyes trying to focus on an otherwise empty sky.
I suspect that many supposed UFO encounters are in fact stars or planets. I'm still curious as to which planet or star it was.