You can also buy a rubber lens hood and push it right against the window. This will keep any reflections down to a minimum and you can usually angle th lens around to get rid of 99% of the rainbow effect you were talking about.
I had good luck with using this technique while flying into Pearl Harbor in Oahu
Aerial View of Diamond Head Crater
All of these were taken out the window of a commercial jet while puddle jumping between Oahu & Maui