I might sound ignorant but I was really amazed this gift from my girlfriend 
The picture below is not the first time I saw it.
At first look, I thought it is an ordinary cup darkened, not showing "I Love You" message clearly. Without the flash, it is even hard to see the texts.
When hot water was poured in the cup/mug, the dark shades will slowly fade. Until the cup/mug turns white, and shows the message clearly. Not only that. Look at the picture below.
This is what made me amazed, and appreciated it more. Our picture shows at the cup. Thanks to