Coffee is pretty famous for having “talent” to stain things. Your Invisalign trays are clear when you start wearing them (the first days in the 2 weeks normal wear time) and it would be nice to have them as clear as possible till the end of those 14 days.
Any stains on the Invisalign aligners will show since it would make them dark and your teeth would look yellowish. This is why (clearly for cosmetic uses, since fewer patients really think about health) it’s important to keep the aligners clean.
I drank coffee myself with the aligners, but most of the time I try to avoid this. I tend to be laxer in the 12th day for instance since I know the aligners will come off and I can abuse them some more. On the other hand, I am not a regular coffee drinker, so it’s not that hard to keep from it.
When I know I have to drink something that would potentially stain my aligners I always think if it’s not possible to take the aligners off and then brush my teeth. Sure, when I am at home NOTHING gets into my mouth with the aligners on. When I meet someone for a talk I try to stick to clear mineral water. I don’t care that much about the stains as I care about the “yucky” taste I’d have in my mouth till I’d be able to clean. The liquid gets under the aligners too and will stay there “decaying” till you brush your teeth and clean the aligners.
So, even if you can drink coffee and wine and coca-cola, it’s a good idea to steer away from when you know you can’t take the Invisalign off. If you are at home, it’s easier, but when in the city, maybe you just don’t want to start cleaning in a public restroom just because you couldn’t keep off the coffee.