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

Downtown Honalulu

All of these were taken out the window of a commercial jet while puddle jumping between Oahu & Maui