ThermoChromic (or ThermoChromatic) inks are designed to offer a visible change in appearance when subjected to temperature.  With a wide range of temperature transitions (-10º C to 60º C), these inks remain a given color until the transition temperature is reached.  At that point the color clears (or disappears), or changes from one color to another.

A 15º C (59º F) transition is an excellent choice for showing a "chilling or cooling" effect.  The 31º C (88º F) is good for body temperature "touch" indication, and a 45º C (116º F) transition is good for "hot" or "burn" indications.  A range of transition inks could produce an visual thermometer effect for many uses.

Pass your cursor over the colors to see the clearing effect.