Each cupcake serves 1.
Line muffin pan with baking cups. Prepare cake mix following package instructions; divide batter in half. With toothpick, add a different icing color to each half. Spoon 1 color batter to the side of baking cup; immediately add 2nd color of batter. Bake following package instructions.
Prepare buttercream icing; divide in half. Tint each half a different, complementary color. Place tip1M into decorating bag. Spoon icing into and up one half of decorating bag; fill second half of bag with second color of icing. Ice cupcakes with 1M swirl.
Apply one or more stripes of icing color with a decorating brush or spatula to inside of decorating bag; fill the bag with white or pastel-colored icing. As the icing is squeezed past the icing color, your decorations will come out striped. Ice cupcakes with 1M swirl.
Ice cupcake with 1M swirl in white or other light pastel colored icing. Spray all or a portion of the icing with food color spray; add additional colors food color spray, as desired.