Living in the desert Southwest, I've never thought about this sort of thing, but who knows - maybe I'll go North someday. Still a very interesting thread since I'm soon to receive my very first colored LED. So here are some dumb questions to add to the mix:
Does it matter whether the ice is more or less opaque? Whether there is any ambient light around? Whether there is any salt, dirt, soot, or rotten squid green stuff in it?