When I was a kid there were mood rings that you could get that 'told' what your mood was based on the color of the ring. Reliant K even had a great song about where all the girls that they knew should wear mood rings.
However I am thinking that we should apply this to neckties. With the nano-technology and such, this should be possible. Red hue for anger, blue for calm, white for totally relaxed, pink for frustrated, etc.