What if the water that came out of the shower was treated with a chemical that responded to a combination of things, like your heartbeat, and your body temperature, and your brain waves, so that your skin changed color according to your mood? If you were extremely excited your skin would turn green, and if you were angry you'd turn red, obviously, and if you felt like shiitake you'd turn brown, and if you were blue you'd turn blue.
Everyone could know what everyone else felt, and we could be more careful with each other, because you'd never want to tell a person whose skin was purple that you're angry at her for being late, just like you would want to pat a pink person on the back and tell him, "Congratulations!"
Another reason it would be a good invention is that there are so many times when you know you're feeling a lot of something, but you don't know what the something is. Am I frustrated? Am I actually just panicky? And that confusion changes your mood, it becomes your mood, and you become a confused, gray person. But with the special water, you could look at your orange hands and think, I'm happy! That whole time I was actually happy! What a relief!
--My favorite excerpt from Extremely Loud and Incredibly Close, by Jonathan Safran Foer