Preheat the oven to 250 degrees F (120 degrees C). Place popped popcorn into a large roasting pan.
Melt butter in a saucepan over medium heat. Stir in sugar, corn syrup, and salt. Cook, stirring constantly, until mixture comes to a boil. Boil, without stirring, for 5 minutes. Remove from the heat.
Stir in food coloring and peppermint extract. Pour over popcorn and stir until well mixed.
Bake in the preheated oven for 1 hour, stirring 2 to 4 times during baking. Remove from the oven and let cool completely before serving, 15 to 20 minutes.