Place popcorn in a large bowl (you'll need room to stir the candy mixture in!)
In a medium pot over medium-high heat, bring sugar, water, and butter to a boil. Reduce heat to medium and boil, stirring constantly, for 3 minutes. Stir in food coloring and salt and pour over popcorn, stirring to coat (make sure you work quickly!). Spread on baking sheets lined with wax paper and let dry for 1-2 hours until no longer sticky.
*This popcorn lasts a long time at room temperature in an air tight container! It'll be good for at least 1-2 weeks.
*I divided my popcorn in 3 to get 3 different colors. I divided my sugar mixture (after boiling) into 3 bowls, then stirred in ½ teaspoon food coloring in each bowl, and pour that over ⅓ of the popcorn each.