Thermochromic inks are pigments that change color to colorless at certain temperature. There are many different types of thermochromic pigments including textile inks for textile screen printing.

Usually you mix normal textile pigments with thermochromic inks so that it looks like the ink is changing from one color to the other. For example, if you mix yellow normal pigment with blue thermochromic ink, you will get green ink that changes from green (under reaction temperature) to yellow (over reaction temperature).

At the Swedish school of Textiles, where Mika is located at the moment, gets thermochromic inks from:

Zenit hantverk
http://www.zenit-konst.se/Servlet
The good thing about this company is that they have smaller quantity (100ml bottles) with affordable price (please ask directly to Zenit about the price list), but they have only 27 degrees reaction temperature inks. The colors come as concentrated pigments and you need to mix with textile binder to print.

B&G color change
http://www.colourchange.com/
They have wide variety of inks with reaction temperature and colors. The bad thing is that their minimum order is quite big quantity (4kg for BPA free ink). Please ask directly to B&G color change for the price list. The ink comes as 1:1 mix with binder.