1. Prepare and bake cake according to package directions, using two greased 9-in. round baking pans. Cool for 10 minutes before removing from pans to wire racks.
2. For frosting, in a large bowl, cream the shortening and sugar
3. until light and fluffy. Beat in the water, salt and vanilla until smooth. Place one cake on a serving plate; spread with 2/3 cup frosting. Top with remaining cake.
4. In a small bowl, combine 2/3 cup frosting and blue food coloring. In another bowl, combine 1-1/2 cups frosting and red food coloring. Fill pastry or plastic bag with 1/4 cup white frosting; cut a small hole in the corner of the bag and set aside.
5. Frost cake top and sides with remaining white frosting. With blue frosting, frost a 3-in. section in the upper left corner of the cake. Pipe white stars over blue frosting. Fill another pastry or plastic bag with red frosting; cut a large hole in the corner of the bag. Pipe stripes across top of cake. Yield: 12-14 servings.