Preheat the oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a large mixing bowl, combine the white cake mix, water, vegetable oil, and eggs. Beat with an electric mixer on medium speed for about 2 minutes until well blended.

Divide the batter into two separate bowls. Leave one bowl as is, and add red food coloring to the other bowl until the desired shade is reached.

Pour the plain batter into the prepared baking pan and smooth it out. Then, pour the red-colored batter over the plain batter and gently swirl with a knife to create a marbled effect.

Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean. Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Once the cake is completely cool, spread the whipped topping evenly over the top.

Arrange the sliced strawberries in the shape of a rectangle in the top left corner to represent the stars of the flag.

Place the blueberries in the remaining space of the rectangle to complete the flag's star section.

Use the remaining strawberries to create stripes across the cake, alternating with the white whipped topping.

Slice and serve your patriotic American Flag Cake!