Make message. If necessary, re-melt tinted candy. Transfer melted candy, separately, to decorating bags. On waxed paper-covered surface, pipe 7 rectangles, all just under 1 in. wide and ranging in length between 2 7/8 in. and 3¼ in. in size. Chill until set, about 5 minutes. Reserve remaining candy in bags.
Using decorating brush and gold metallic paint, draw HOORAY! message on candy (one letter per rectangle). Using any remaining light blue icing, attach candy pieces to side of 6 in. cake.