I have seen them from Anchorage in October-November, but having to be at work at 7:00 am, didn't have the luxury of getting out lawn chairs and having a beer! Like others have said, these were primarily just green dancing curtains, not the full color kind.
Saw the colored ones once when I happened to be in Anchorage for meetings the same weekend that the Iditarod started on a downtown street. Because the race is near the spring equinox, the lights are often visible during that week. So, the closest thing you might have to a "sure bet" would be to take a trip to Alaska to watch the Iditarod.