Gel

Gels are the only things in the game that can alter materials (besides the editor). If a token steps on a gel, the token changes material to the gels material, and the gels use count goes down one step. If a gel is set on fire the whole gel is consumed, no matter the use count and the material of the tile beneth is changed to the material of the gel.

Trivia
There was once an idea to have black and white gels to change white/black status, but that idea was disregarded because it seemed too over powered.