Stir 2 cups of the boiling water into each flavor dry gelatin mix in separate medium bowls 2 min. or until completely dissolved. Stir 1 cup cold water into gelatin in each bowl. Refrigerate blue gelatin 1-1/2 hours or until thickened (spoon drawn through leaves definite impression).
Let strawberry gelatin stand at room temperature.
Add blueberries to thickened blue gelatin; stir.
Pour into 4- to 6-qt. glass bowl. Refrigerate 30 min. or until set but not firm (gelatin should stick to finger when touched and should mound).
Spread with 3-1/2 cups of the whipped topping; refrigerate. Meanwhile, refrigerate strawberry gelatin 1-1/2 hours or until thickened. Stir in strawberries; spoon over whipped topping layer.
Refrigerate 3 hours or until firm. Top with the remaining whipped topping. Store in refrigerator.