Place popcorn in a very large bowl. In a small saucepan, melt butter. Stir in the sugar, corn syrup and salt. Cook and stir over medium heat until mixture comes to a boil. Reduce heat to medium-low; cook 5 minutes longer, stirring occasionally.
Remove from the heat. Stir in vanilla and food coloring. Pour over popcorn; toss to coat. Transfer to two 15x10x1-in. baking pans coated with cooking spray.
Bake at 250° for 45 minutes, stirring every 15 minutes. Spread on waxed paper to cool. Store in airtight containers.