This is one of the better uses I’ve seen of heat-sensing materials:

It’s a tub painted by Alsacorp. Now, instead of this disgusting radioactive-waste colored thing, imagine a tub that turned from white to an attractive shade of azure blue when it was just the right temperature to step into. Or perhaps we could get some cooking pots that would show their temperature by color. For example, don’t touch a handle that has turned red. Even better would be servers and racks, or similar heat-sensitive equipment, painted to show current heat-levels. (you saw it here first) Anything running red, for example, would need more localized cooling. Immediate improvements would be realized as the paint changed its shade.

More information is good, and choosing the right color is probably important if you don’t want to bother with specialized training. I figure most people (including me) see lime green water as a rather unattractive sign for a bathtub no matter how helpful it is to know the temperature.