HEAT oven to 350ºF.
PREPARE brownie batter as directed on package; spread onto bottom of 12-inch pizza pan sprayed with cooking spray. Bake 15 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool 30 min.
ADD food colorings to COOL WHIP; stir gently until well blended. Spread over brownie; top with remaining ingredients.
CUT into wedges.