Preheat oven to 225 degrees. Prepare a large, rimmed baking sheet with parchment paper spritzed with non-stick cooking spray.
Spread popped popcorn over the baking sheet and salt, if desired.
In a medium saucepan, combine the sugar, corn syrup, and butter. Cook over medium-high heat for 3 minutes, stirring occasionally.
Remove from heat and stir in the Kool Aid and baking soda until combined.
Pour over the popcorn and toss the popcorn to coat.
Bake for 40 minutes, stirring every 10 minutes.
Allow to cool completely before breaking into pieces.
Store in an airtight container.