1. Heat oven to 350Â°F (325Â°F for dark or nonstick pans). Grease or spray bottoms only of three 8-inch or 9-inch round pans.
2. Make cake batter as directed on box. Pour 1 1/2 cups of the batter into small bowl. Pour another 1 1/2 cups of the batter into one of the pans.
3. Stir 6 to 10 drops red food color into batter in small bowl. Stir 6 to 10 drops blue food color into batter in large bowl. Pour pink batter into another pan; pour blue batter into remaining pan. (If necessary, refrigerate 1 pan of batter until ready to bake.)
4. Bake 17 to 22 minutes (19 to 26 minutes for dark or nonstick pans) or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling rack. Cool completely, about 1 hour.
5. Brush crumbs off cake. Place blue layer, top side down, on plate. Spread 1/3 cup frosting on blue layer almost to edge. Place white layer, top side down, on frosted layer. Spread 1/3 cup frosting on white layer almost to edge. Place pink layer, top side up, on frosted layer. Frost side and top of cake with frosting. Store loosely covered.