Place the butter, sugar, and corn syrup in a small saucepan over low heat. Stir frequently until the butter melts and the sugar dissolves. When the mixture begins to boil, remove from heat. Add the baking soda and mix well. Add the cinnamon oil to taste and 2 to 4 drops of red food coloring if desired. The best color is a medium pink.
Place the popped corn in a large bowl. Pour the mixture over the popped corn and gently stir to coat. Turn the popped corn onto 2 baking sheets. Bake at 250 degrees for 45-60 minutes, turning the mixture every 15 minutes.
Remove the cinnamon popcorn from the baking sheets to cool and store in an airtight container.