Check out this sweet LED faucet attachment. (Yes, I know I'm a nerd.) You can buy it at ThinkGeek.com. Simple to install and GREAT for getting three year olds to want to wash their hands and brush their teeth.
Probably also great for stoners, but, you know, whatev.
Oh yeah, and it changes from blue to red when the water temp hits 89 degrees. Here are some shots with the lights on and off. Warning, with the lights off this just might blow your mind.