These are the first genetically modified pets, sold under the name GloFish. They are zebra fish tweaked with genes from other, exotically colored creatures such as jellyfish. The GloFish are fluorescent, and in a dark room will glow under ultraviolet light.
Genetically modified animals are now under various legal strictures -- the GloFish were developed earlier, and at least in the U.S. are still permitted under a sort of "grandfather clause." It's unlikely we'll actually see a purple cow, and I'd rather see than be one, but I thought the GloFish would be a cheering sight for those of you living under gray skies on this first day of '08. Happy New Year!