Prepare the cake mix as per package instructions. Separate evenly into three bowls of about 1 ½ cups batter each. Color one bowl red, and one blue. Gently stir color into batter. Pour into three loaf pans that are lightly greased and lined with a parchment sleeve. Bake for 10-15 minutes, until a toothpick inserted into the center of the cake tests clean. The cakes should be fully cooked through. Allow to cool completely.
Using a 1-inch biscuit cutter, cut 8-10 circles out of each of the cakes. Gently brush the outside of each of the cut-outs with simple syrup and then coat in sanding sugar. Let the cut-outs dry for 10 minutes before assembling.
Dab a ¼-½ teaspoon of frosting on each of the red cakes, and then top with a white cake. Dab with another ¼-½ teaspoon of frosting and then top with the blue cakes. Using a straw, cut a hole through the center of the cakes, discard. Fill the cakes with popping candy and top with a 1-inch length of black licorice. Serve within an hour.
TIP: Letting the sanding sugar dry is necessary to prevent the colors from bleeding.