Preheat oven to 225 degrees F. Line a baking sheet with foil and spray with non-stick cooking spray, then set aside. Measure out each flavor and baking soda and set them aside.
Place 1 bag of popcorn in a large bowl and set aside.
Place the butter, corn syrup, and sugar in a small saucepan and heat, stirring constantly, to boiling. Cook for 1 minute. If you start to smell anything caramel-y, remove from heat immediately. Stir in the first flavor/baking soda and stir to combine evenly. Pour over the popcorn in the bowl and toss quickly to coat the popcorn evenly. Transfer the popcorn to the prepared pan. You should be able to fit two batches onto one pan (three if you’re really feeling cheeky.)
Wash the bowl and pan immediately in hot water and then repeat twice with the remaining ingredients (each batch takes less than 10 minutes). Bake for 20 minutes in the preheated oven, stirring once. Remove from oven and allow to cool.
To make the popcorn boxes, purchase blue, green, and pink popcorn boxes from a party supply store. Print out the linked printable (linked in post) and carefully cut out each decal. Glue all the way to the edges with a gluestick, then apply to the front of each bag, pressing all the way to the edges. Allow to dry before filling with popcorn.