re: FOX, seen today's APOD
Thanks, Steve!
The one I got to see on live TV last week was very like that one. The helicopter was at the proper angle to catch the rainbow in the shot, and the twister was white becuase the sun was shining fully on it from beyond the edge of the supercell.
If you've got Windows Media Player you might be able to watch the edited version from here. It's the last item on the "Top Stories" list. It was a lot more fascinating to see the whole development, but there's a great rainbow shot toward the end.