Blue is Cold, Red is Hot
Isn't it amusing that "cool" and "hot" are both positive adjectives for something trendy or fashionable? You can use the words in their most literal sense here:
Look at Inhabitat.com or MoCo Loco for more pictures.
Hansacanyon's temperature sensitive backlighting uses LEDs that change color as a function of water temperature so you can see when it's hot or cold.