Make cupcakes. Prepare white batter following recipe directions. Tint portions of batter 1/3 red and 2/3 green.
Place two-tone insert in baking cup-lined muffin pan. Use a cut disposable decorating bag to fill center ring of insert 2/3 full with red batter. Use a cut disposable decorating bag to fill outer ring of insert 2/3 full with green batter. Remove insert and repeat until all cavities are filled. Remove insert. Bake and cool.