Think Geek introduced their low-cost LED faucet light back in 2006. Back then it would only light up your water stream from the faucet in blue.
The new version is now temperature sensitive and changes from blue LED light to red when the water hits 89 degrees.
The Blue/Red LED faucet light sell for $19.99 on Think Geek.
The blue LED only faucet light is also still available for $12.99.
The LED faucet light comes with two universal adaptors which make it fits most standard faucets in USA.