The butter on your movie theater popcorn isn't butter. At most theaters the pump is filled with buttery topping, which is soybean oil, artificial butter flavor and beta carotene, the same pigment that makes carrots orange.
It can't be sold as butter. Federal law has defined butter since 1923. It has to be made from milk or cream, with nothing added but salt and color, and be at least 80% milkfat. That's why the jug the theater buys says buttery topping or butter flavored topping. Some brands also add TBHQ and citric acid to keep the oil from going rancid, and FDA caps TBHQ at 0.02% of the oil.
At a lot of theaters the popcorn is yellow before the topping ever touches it. Gold Medal's Flavacol popcorn salt goes in the kettle, and its ingredient list is salt, artificial flavor, Yellow 5 Lake and Yellow 6 Lake.
Some theaters do use real butter. Odell's sells theaters a real butter topping with the water and milk solids taken out, so it can ship without refrigeration.
Just found AMC popcorn has 0% butter and it’s just soybean oil dyed yellow with artificial flavor 🤮