hahaha no no that mug is actually my coffee ground holder. I dont have a knock box, so i just scoop the grounds out of the portafilter into the mug and I empty the mug once a week. The ground usually dry out quick enough so they dont mold. I only ever has 1 issue with mold and that was when I ran a single shot through my double shot basket, so there was a lot of excess water.
But yes, I agree, only black. I make my guests use milk if they want something else in their coffee.