Add 1-1/3 cups boiling water to 2 pkg. gelatin mixes in medium bowl; stir 2 min. until completely dissolved.
Pour into 8-inch-square dish sprayed with cooking spray. Refrigerate 25 to 30 min. or until gelatin is set but not firm.
Meanwhile, add remaining boiling water to remaining gelatin mixes in medium bowl; stir 2 min. until completely dissolved. Stir in evaporated milk. Refrigerate 15 min. or until slightly thickened; pour over gelatin layer in dish.
Refrigerate 4 hours or until firm. Unmold onto cutting board just before serving; cut into 4 rows, then cut each row into 7 alternating triangles.
Garnish with sprinkles. Reserve gelatin trimmings for snacking.
