Preheat oven to 350 degrees.
Prepare cake batter as directed on box.
Divide batter into 2 bowls.
Tint 1 red and 1 blue. Bake as directed on box, then cool.
For Ice Cream: Whip cream until stiff peaks form. In another bowl, whisk together milk, vanilla, and sweetened condensed milk until combined.
Pour over cream and gently fold together until mostly combined, taking care not to deflate cream.
Crumble in 4 red cupcakes and 4 blue cupcakes and stir gently. (Reserve remaining cupcakes for another use).
Pour mixture into shallow dish and freeze 6 hours until firm.
