Preheat oven and line muffin tins with paper liners.
Prepare batter according to box directions.
Add just a touch of yellow color and enough red to achieve watermelon pinkish color.
Fold in chocolate chips until distributed.
Fill liners 2/3 full and bake according to box directions for cupcakes.
Allow to cool completely.
Whip butter and vanilla for until fluffy.
Gradually add powdered sugar.
Add milk until you reach desired consistency.
Transfer to piping bag with round tip and frost each cupcake.