To frost, place each color in individual resealable food-storage plastic bag. Cut 1/2 inch off 1 corner of each bag, and pipe each frosting on corresponding color cake layer. Pipe a dot of frosting and use back of table spoon to spread frosting horizontally around cake, with deepest color at bottom and working up to lighter colors; repeat around cake slightly overlapping dots of frosting. To frost top, use remaining frosting as desired. Store cake loosely covered in refrigerator.