i would suggest covering your cake in white marshmallow fondant, then painting the black cow spots. i just painted on fondant for the first time over the weekend, and it was super easy. just take your black gel coloring and add some vodka or everclear to it and paint right on the cake. the alcohol will evaporate off, so there won't be any alcohol taste leftover. if you are covering the cupcakes with fondant, it is easy to color. i have only ever added coloring after the fondant is made. but, i have heard that you can add the coloring once the marshmallows are melted, before you add the powdered sugar, but like i said, i've never tried it that way. good luck and be sure to post a pic when you're done.