1. Prepare cake mixes according to package directions. Grease and flour two 9 x 13-inch pans. Divide cake mixes among two pans. Bake 45 minutes, or until skewer inserted comes out clean. Let cool completely.
2. Divide all frosting among three bowls. From one bowl, transfer 1/3 cup frosting to resealable plastic bag; tint remaining frosting in bowl yellow. Tint second bowl blue; tint third bowl orange.
3. Cut one 4-inch, one 5-inch, and one 6-inch circle from each cake. Trim tops of cakes to make level. Layer 6-inch cakes, and frost with orange frosting. Repeat with blue frosting for 5-inch layers and yellow frosting for 4-inch layers. Refrigerate cakes 30 minutes.
4. Place the orange cake on a serving plate. Top with blue cake, then yellow. Place trimmed skewer through centers of layers to secure. Transfer remaining frosting to resealable plastic bags, and snip off corners; pipe decorative patterns of frosting onto sides.