Make 2 boxes of your favorite white cake mix. I use gel food coloring because the color is deep and true. You can get it at craft supply store or order it online. Get your batters to your desired colors. Remember though that it will bake a touch darker.
Pour the blue batter on the bottom.
Add the white layer, then cover the top with red. Spread the red layer over top so it covers the white completely.
Make a batch of cream cheese frosting. (I used 1 stick of butter, 1 brick of cream cheese, 2-3 cups powdered sugar, a teaspoon or so of vanilla. Beat until light and fluffy.) You could always use a canned frosting too.