1Heat oven to 350°F (325°F for dark or nonstick pans). Make, bake and cool cake as directed on box for two 8-inch or 9-inch rounds.
2Reserve 1/4 cup of the frosting. Place 1 cake layer, rounded side down, on serving plate. Spread with about 1/3 cup frosting. Place other layer, rounded side up, on top. Frost side and top of cake with remaining frosting.
3Position stencil on top of cake. Sprinkle colored sugars over stencil, being careful not to mix colors or get sugar on other areas of cake surface; remove stencil. Tint reserved 1/4 cup frosting with 2 drops of desired food color. Place frosting in decorating bag with writing tip #4. Pipe desired message on cake. Pipe design on edge of plate if desired.