Reader Jason sends in this heat-changing paint from Alsa Corp. By applying a certain type of Eclipse paint, the finish will change from one color to another—white to blue, black to green, black to Apple Red Candy—whenever heat is applied.
Splashing this on your shirt and re-living the late '80s aside, the paint has a few interesting applications. Jason notes of placing these on a case or a laptop so you can know which parts of the system is the hottest. There's also uses in sinks, bathtubs, and walls, for telling the temperature at a glance.
Product Page [Alsa Corp - Thanks Jason!]