PREPARE cake batter and bake as directed on package for cupcakes. Cool in pans 10 min. Pierce tops with fork.
ADD boiling water to gelatin mix in small bowl; stir 2 min. until completely dissolved. Spoon over cupcakes. Refrigerate 30 min. Remove from pans.
TINT COOL WHIP with food coloring; spread over cupcakes. Top with marshmallows. Decorate as desired.