PREPARE cake batter and bake in 13x9-inch baking pan as directed on package. Cool 15 min. in pan; remove cake to 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 enough food colouring to create a light yellow colour; use to frost palette area left by template outline.
POSITION paint brush in centre of palette; arrange different coloured candy wafers on cake (as shown in photograph) to resemble blobs of paint on the paint palette. Store in refrigerator.