How it works?
There are some thermochromatic materials that allow for the color to be set in a stable way allowing for a persistent change in color after the material is heated beyond a particular set point. An example of this property can be seen in erasable pen products. Erasable pens use heat generated by friction to make the ink transparent. To make the ink visible again all one has to do is freeze the paper and the color will be restored to the ink.
The thermochromatic materials we are using have two temperatures that trigger a color change. One is below freezing and the other is within the printable temperature of the particular plastic being used. This makes it possible to print the material and selectively change the color of portions of the print just by changing the temperature of the hot end.