Here is the first of hopefully many posts highlighting some spur-of-the-moment cupcake production
So the frosting looks complicated, but really it can be done with a ziplock and some patients. Make some plain american-style buttercream frosting (2 sticks butter, 4 cups powdered sugar, some vanilla and a few tablespoons milk). Divide the frosting into 4-6 bowls. Add food coloring to each bowl making a few different colors. Carefully place each colored frosting, side by side, in a pastry bag or ziplock. You want basically a color wheel of frosting inside your one pastry bag. If your frosting seems a bit too soft stick it in the freezer for 5-10 minutes. Cut off the tip of the ziplock, the smaller the whole, the more color you will get! Try to cut a whole in your bag so a pea would just barely be able to fit through.