1Heat oven to 350°F (325°F for dark or nonstick pans). Grease and lightly flour bottom and side of 9-inch round cake pan, or spray with baking spray with flour. Place paper baking cup in each of 12 regular-size muffin cups.
2Make cake batter as directed on box. Pour half of batter in round pan; spoon remaining batter into muffin cups. Bake as directed on box. Cool completely, about 1 hour.
3In small bowl, place 1 tablespoon of the frosting; stir in 1 drop yellow food color. In another small bowl, place 1/4 cup frosting; stir in 2 drops red food color. In third small bowl, place 1/2 cup frosting; stir in 4 drops blue food color.
4On serving plate, place cake layer with rounded side down. Frost top and side with white frosting. Frost 7 cupcakes with blue frosting, 4 cupcakes with pink frosting and 1 cupcake with yellow frosting. Place 1 blue cupcake on center of white frosted cake. Place remaining blue cupcakes, sides touching, in circle around center cupcake. Place 2 rows of 2 pink cupcakes on top center of blue cupcakes. Place yellow cupcake on top center. Sprinkle with candy sprinkles. Store loosely covered.