Bake a white cake in a 13x9 inch pan according to package instructions. Remove from oven and then allow to cool.
Using a fork, poke holes in the top of the cake.
Mix together the blue and red gelatin each with 1 cup of boiling water until dissolved, and then spoon each color gelatin over the cake, making sure to pour over the holes. The best way to do this is a row of blue, then a row of red and alternate so you get a colorful mix of red and blue in the cake. It's good to spoon over each row 2-3 times for good coverage.
Then mix together cream cheese and powdered sugar with 2 tablespoons of milk. Mix in the whipped topping.
Spread cream cheese mixture over the cake.
Top with rows of strawberries and blueberries.
Chill for 4 hours before serving.