HEAT oven to 350°F.
PREPARE cake batter and bake as directed on package for 24 cupcakes. Cool in pans 10 min. Remove to wire racks; cool completely.
BEAT pudding mix and milk with whisk 2 min. Stir in green food coloring; spoon into pastry bag fitted with round tip. Refrigerate until ready to assemble cupcakes. Cut cone-shape piece from top of each cupcake. Pipe 1 Tbsp. pudding into each cupcake; replace cupcake top.
STIR food coloring into frosting; spread onto cupcakes. Decorate with remaining ingredients as shown in photo.
Make Ahead: Cupcakes can be decorated ahead of time. Refrigerate up to 8 hours before serving.
If You Don't Have a Piping Bag: Fill a resealable plastic food storage bag with pudding mixture; seal bag. Cut one corner off bottom of bag, then use to squeeze pudding mixture from bag into cupcakes.