This was taken on 17/01/06 - apparently the colours were so vivid because of a volcano erupting on the other side of the world and dust particles being thrown in atmosphere..
I noticed it too that day and tried to take a few snaps... mine just aren't as impressive as yours though (oh and I'm too lazy to walk down the stairs to get them off the iMac)
Nice picture. I remember Tuesday's sunset being especially vivid – volcanic dust particles, then? My desk at work gives me a pretty good view of the western sky through the skylight, but after a long and tiring day I had neither the inclination or the energy to go and get the camera.