Preheat the oven to 350°F Grease and flour two 8-inch round cake pans or see Tip #1 below.
Prepare the cake mix batter according to package directions.
Pour 1 cup batter into each prepared pan. Drop 5 to 7 drops each of the red and blue food coloring randomly on batter. (I found the larger the drop pools, the better the effect. In other words, don't skimp or there will not be enough gel effect when cutting the cake.) Swirl the coloring with a wooden skewer. Divide the remaining batter evenly between the pans, spooning batter gently on top of swirled colors. Drop 5 to 7 drops each of red and blue food coloring randomly on the batter again; swirl coloring with a wooden skewer.
Bake the cakes until a toothpick inserted in centers comes out clean, 30 to 35 minutes. Cool the cakes in the pans on wire racks for 10 minutes. Remove the cakes from the pans and place on wire racks to cool completely.
Place one cake layer on a serving plate. Spread the top with about 3/4 cup frosting. Top with the second cake layer. Spread the side and top of the cake with the remaining frosting. Draw several sets of concentric circles on top and side of cake with the red and blue decorating gels. Drag a wooden skewer through the circles to feather the colors and make bursting fireworks designs.
Two Tips To Remove Cake From Pans:.
Tip 1. An easier method is to outline 2 pieces of wax paper cut to the size of the bottom of the cake pan. Place wax paper on bottom and pour batter over. When inverting after baking, immediately peel off wax paper and dispose.
Tip 2. Let each cake layer cool in the pan for 10 minutes before removing; the cake will release steam and begin to pull away from the pan edge.
Check to see if the cake will come out easily by placing one hand on top of the cake and carefully inverting the pan. If the cake layer doesn't release, run a knife around the edge of the cake to help loosen. Place your hand on the top and carefully invert the pan again. Remove the cake and carefully place on a rack to cool completely.