PLACE 1 cookie in each of 24 paper-lined muffin cups. Prepare cake batter as directed on package; spoon over cookies. Bake as directed on package for cupcakes. Cool in pans 10 min.; remove to wire racks. Cool completely.
SPOON frosting into bowl; stir in food colorings. Arrange cupcakes on large plate to resemble pumpkin shape with stem. (See photo.) Reserve 1 tsp. frosting; spread remaining frosting onto cupcakes. Sprinkle colored sugar around edge.
CUT 2 of the remaining cookies in half; place, cut-sides up, on pumpkin stem. Cut each of 3 of the remaining cookies into thirds; arrange on cake for the jack-o'-lantern's eyes, nose and mouth. Cut remaining cookie in half; use for the eyebrows. Decorate cake with candy corn as shown.