Review on 🥤 Spectrum Unbreakable Assorted Plastic Tumblers: Durable and Stylish Drinkware for Every Occasion by Demetrius Young

They're cute and I really like them. I'm curious if anyone else experiences this: I've had them for a few weeks now and have been used/washed in the dishes a few times. I've noticed that there is some sediment on the inside and outside of each cup when clean (I'm attaching a couple of photos). It comes off very easily if I run my fingers lightly over it. Anyone know what it is? EDIT: Actually I was looking at the stack of little cups that we haven't used yet (because they're so tiny) or washed up and they have leftovers too!