Using a long serrated knife, trim rounded top of cake flat. Invert cake and place on a large flat tray or serving platter. Trim sides of cake to make a large jelly bean shape. Using a melon baller or cookie scoop, make a round, shallow indentation in top of cake for the palette's finger hole.
Transfer 2 cups of the Creamy White Frosting to a medium bowl. Add Chocolate Butter Frosting; stir slightly to swirl frostings together. Spread swirled frosting over top and sides of cake. With some of the remaining white frosting, spoon 1 tablespoon frosting each into five or six small bowls or custard cups. Tint each portion a different color using food coloring (make sure to tint one portion black). Spoon black frosting into the hole, spreading the frosting inside the hole to cover the cut edges. Arrange each of the remaining colored frostings on top of cake, spreading each color slightly with the back of spoon. If desired, sprinkle with colored sugars.
For paintbrush, use scissors to cut fringe into one edge of fruit leather strip. Wrap strip around breadstick, about 1 inch from one end. Place on top of cake.