Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large mixing bowl, combine the cake mix, water, vegetable oil, and eggs. Mix according to package instructions until well combined.

Divide the batter evenly into three separate bowls. Leave one bowl plain, add red food coloring to the second bowl until you achieve your desired shade, and add blue food coloring to the third bowl to reach your preferred color.

Pour the plain batter into one prepared cake pan. Carefully pour the red batter into the second pan. Bake both cakes in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Once baked, remove the cakes from the oven and let them cool in the pans for 10 minutes. Then, transfer them to wire racks to cool completely.

Once the cakes are completely cooled, place the red layer on a serving plate. Spread a layer of whipped cream on top, then add a layer of sliced strawberries.

Place the white cake layer on top of the strawberries, then spread more whipped cream on top. Decorate with blueberries and any remaining strawberries.

Chill the cake in the refrigerator for at least 30 minutes before serving to allow the flavors to meld.