Cool! er, Hot!
“Temperature-Sensitive Glass Tiles
Long story short: "Textured glass tiles that alter in color with changes in temperature."
For a change, not a concept or "real soon now" but ready today for whatever you'd like to do with them.
About $15 per standard size 4" x 4" x 3/8" tile.
So a square foot will run you about $150.
No end of fun.