Moving Color has a line of tiles that are inspired by the Nothern Lights. The glass tiles appear black in room temperatures, but move throught the colour spectrum when warm water is applied. Each tile is 4 x 4 and a square foot will cost about $180.
Implications - If you're planning on redoing your bathroom, these tiles are the obvious choice for your new shower. Showering will be a whole new experience once these color changing tiles are installed. Who wants to be surrounded by plain white, boring walls when they could be engulfed by the aurora borealis? You will probably be taking more showers with these up.