1. Bake cupcakes according to package directions. Meanwhile, prepare buttercream frosting and tint with green food coloring.
2. Spread frosting over cooled cupcakes. Optionally, pipe grass onto the top of each cupcake.
3. Cut about 1 to 1/2 inches from each rainbow strip - otherwise they will be a little too long. This also provides a great snack while you are making the cupcakes. Press each end of the rainbow into the top of the cupcake, as pictured. Gently press a few miniature marshmallows into the frosting around the ends of the rainbow, to form the clouds. Sprinkle on the gold.