What is the mug icon?

[Digihuman]

I just had a terrible day running the tavern after I'd made my first beer available. The game doesn't give me a popup about what the new icons appearing over my patrons' heads is.

So it looks like a mug and it's either green or blank? What does that mean? I tried serving these people beer but it wouldn't let me, so that can't be it, then my customers got mad at me and left and I lost reputation.

[☣[6e3gapH0cTb]☣]

When you have prepared beer (tea, water, wine, etc.), and it has been pulled out in a barrel, you usually pour it into a special container for serving to guests. It can be a large barrel in the wall behind the bar, or one of the 4 taps located on the bar itself. For ease of orientation between your drinks, the taps are marked with certain colored circles. You can change the color by opening the storage inventory for the finished liquid. So, when guests place an order not at the bar, but from their table, an icon with a mug and a colored circle appears above their head. The color of the mug of the drink they ordered coincides with the one that is poured into the storage with the same color of the mug. You can also see when guests place an order at the bar, the icons of the drinks themselves appear on top, but for convenience, the color corresponding to the storage is also drawn there, where the same drink is stored. In the future, the number of barrels, as well as the drinks themselves, will be very large and diverse, these associations with colors will help you not get confused in the huge selection of your drinks. PS I don't know English very well, I used a translator to write this answer. if you have any questions, I will try to answer them. Don't judge me if it was misspelled.