Preheat the oven to 350°F and lightly grease or line a 9x13 inch baking pan with parchment paper.

In a large mixing bowl, combine the cake mix, egg, melted butter, and heavy cream until smooth.

Spread the batter evenly into the prepared baking pan and bake for 20-25 minutes, or until a toothpick inserted comes out clean.

Allow the baked layer to cool completely before frosting.

To prepare the frosting, beat together the cream cheese and butter until smooth, then slowly add the powdered sugar, heavy cream, and vanilla until fluffy.

Divide the frosting into two bowls. Mix purple coloring into one and blue into the other.

Spread the colored frostings alternately over the cooled layer and swirl with a spatula.

Decorate with sprinkles, cut into bars, and serve.