Have you remembered the Pac-man mug that can hide all characters including ghosts and Pac-man through the hot water? Here is another mug adopting this principle.
It’s called Switch ON/OFF Mug. unlike the pac-man mug, this mug prints the symbols of ON and OFF. Once you pour the cool beverage into it, the surface of the mug will completely turn into black and display the OFF. The hot water will make the mug become white, and the OFF switches ON.
Switch ON/OFF Mug is priced at $16 USD. If you are finding a fun mug for your coffee time in office. take a look the mug at Brando.