This is actually reminiscent of a Doctor Who mug i had when i was a child. The mug was completely white if empty, but any hot liquid inside would make a blue tartis appear. This began my fascination with specialty inks. Too many trips in the microwave, however, put the tartis’s trips to my lips to an end. The mug is forever an empty white now, and has retired to hold pens. RIP, 80’s era Tartis Mug.

via Mug with a temperature sensor.