Melt butter. Stir in sugar, corn syrup and salt. Cook and stir over medium heat until boiling. Reduce heat to medium low, cook 5 min., stirring occasionally. Remove from heat and stir in vanilla and food coloring. Adjust food coloring as needed (optional). Pour over popcorn, toss.
Place into baking pans, sprayed with cooking spray. Bake at 250 for 45 min., stirring every 15 min. Spread evenly to cool.