PREPARE and bake cake mix as directed on package for 13x9-inch baking pan. Cool 5 minutes in pan; remove cake to a cake board or tray. Cool completely.
MAKE a template drawing of an artist's palette as shown in photograph using wax paper; place on top of cake. Frost remaining cake with 2 cups of the whipped topping; remove template.
TINT remaining whipped topping with food coloring to create a light yellow; frost palette area left by template outline.
POSITION paint brush in center of palette; arrange different colored candy wafers on cake (as shown in photograph) to resemble blobs of paint. Refrigerate until ready to serve.