Add 1 cup boiling water to lemon gelatin mix in medium bowl; stir 2 min. until completely dissolved. Stir in 1/2 cup cold water.
Pour into 8-inch square pan. Refrigerate 4 hours or until firm.
Stir remaining boiling water into orange gelatin mix in large bowl 2 min. until completely dissolved. Stir in remaining cold water. Refrigerate 20 min. or until slightly thickened.
Cut lemon gelatin into 1/2-inch cubes or decorative shapes.
Add to orange gelatin along with the COOL WHIP; stir gently until blended. Refrigerate until thick enough to mound; pour into crust. Refrigerate 4 hours or until firm.