ADD water to gelatin mixes and rose petals; stir 2 min. until gelatin is completely dissolved. Cover with plastic wrap. Let stand 15 min. Drain; discard petals.
POUR 1-1/2 cups gelatin into 6-cup mold sprayed lightly with cooking spray. Refrigerate 30 min. or until gelatin is set but not firm. Meanwhile, let remaining gelatin stand at room temperature.
MIX remaining gelatin and milk. Gently pour over gelatin layer in mold. Refrigerate 3 hours or until firm. Unmold dessert onto serving plate. Serve topped with COOL WHIP.