This is Probably Pumpkin Spice - Color Changing Mug - Reveals Secret Message w/ Hot Water.
The mug starts out a glossy black color. When hot liquid is added the brilliant color message appears and the mug turns white! Surprise your friend with a secret message.
To see it in action click here! https://youtu.be/aHIL4X4luPY
Available in 11oz.