Preheat the oven according to the cake mix instructions.
Prepare the cake mix by combining the cake mix, water, vegetable oil, and eggs in a bowl.
Pour the batter into a greased 9x13 inch baking pan and bake as directed.
Once baked, let the cake cool completely.
Poke holes in the cooled cake using a fork.
Prepare the blue Jell-O according to package instructions and pour it over the cake, allowing it to seep into the holes.
Repeat the process with the red Jell-O.
Refrigerate the cake for at least 4 hours or overnight.
Top with whipped topping and garnish with fresh strawberries and blueberries before serving.