PREPARE cake batter and bake as directed on package for 1 (9-inch) round pan and 1 (9-inch) square pan. Cool completely.
LEAVE round cake whole; cut square cake as shown in diagram. Arrange cake pieces on cutting board, platter or tray as shown in photo.
STIR food colorings into COOL WHIP; spread onto cakes. Decorate with cookies and candies as shown in photo.