Preheat your popcorn maker or heat a large, heavy-bottomed pot on medium heat. Add a few popcorn kernels and wait until they pop, signaling the pan is hot enough. Add the remaining kernels, cover with a lid, and shake occasionally until all kernels are popped and fluffy, then transfer to a large mixing bowl.
In a medium saucepan, combine sugar, corn syrup, butter, and salt over medium heat. Stir constantly with a spatula or wooden spoon until the mixture comes to a gentle simmer, about 3-4 minutes. Continue stirring until the sugar dissolves completely and the mixture begins to thicken slightly, with a clear, glossy appearance.
Remove the saucepan from heat and divide the glaze into three portions. Add blue food coloring to one portion and red food coloring to another, mixing each until the color is vibrant and evenly distributed. Keep the third portion plain for later coating.
Pour the plain glaze first over the popcorn, gently tossing or stirring to coat evenly. Then, drizzle the red glaze over one section and the blue glaze over another, mixing gently to create colorful swirls and patches. Use a spatula or your clean hands to ensure all popcorn is coated in a shiny, sticky layer of glaze.
Spread the coated popcorn mixture onto a baking sheet or large plate in an even layer. Let it sit at room temperature for 10-15 minutes until the glaze hardens and forms a crisp, shiny coating.
Once the glaze is set, break apart any clusters if necessary and transfer the popcorn to a serving bowl. Serve immediately or store in an airtight container for up to 2 days, maintaining its crunch.
