I thought this was a really cute idea so decided to try it out. I halved the recipe for Magnolia Bakery's vanilla cupcakes so I would get just one dozen instead of two (although I ended up with 14). I added 10 drops (give or take a drop) of red food coloring and 1/4 cup plus about a tablespoon more of mini chocolate chips.
I then used a watermelon frosting recipe I found here, though was disappointed that the frosting was too liquidy to pipe at all, even after refrigerating it for a while. It does taste nice, however! Oh, and I added green food coloring to the frosting as well.