I don't usually post anything about tile, but this has my attention. Moving Color manufactures several different temperature sensitive tiles for the bathroom (or any other tile application).
Custom creations are not a problem. "Choose your texture, color and temperature range and we will give life to your project."
They even make a touch sensitive tile!
I've never used these tiles and can't really endorse them but it's another interesting find out on the interwebs! ;)