Heat oven to 325°F. Generously grease 12-cup fluted tube cake pan with shortening or cooking spray. Make cake mix as directed on box, using water, oil and eggs. Pour half of the batter into medium bowl; set aside. Divide the other half of batter equally between 2 small bowls. (You will be left with 3 bowls of batter.) Add red food color to 1 of the small bowls and mix well. Add green food color to the second small bowl and mix well.
2Pour half of the white batter from medium bowl into cake pan. Carefully pour red batter over white batter in pan. Carefully pour green batter over red batter. Then pour remaining white batter from medium bowl over the top. Do not mix the colors.
3Bake as directed on box until toothpick inserted near center comes out clean. Cool 10 minutes. Turn pan upside down onto cooling rack placed over a cookie sheet; remove pan. Cool completely, about 30 minutes. Place cake on serving plate.
Divide frosting between 2 small microwavable bowls. Microwave 1 bowl on High about 5 to 10 seconds; mix well with spoon until smooth enough to drizzle. With the spoon, drizzle white frosting back and forth around the whole cake in a striping pattern until you use all of the frosting (allow some frosting to drip down onto plate in middle of cake, if desired).
5Microwave second bowl of frosting; stir in a few drops of green food color. Drizzle over cake, scattering back and forth in the same type of striping pattern. Decorate with sprinkles. Let stand until frosting is set before serving.