PREPARE and bake cake batter as directed on package for 24 cupcakes; cool completely in pan. Pierce cupcakes with wooden skewer or large fork at 1/4-inch intervals. Add boiling water to jelly powder; stir 2 min. until completely dissolved. Spoon over cupcakes, adding about 2 tsp. to each. Refrigerate 3 hours.
TINT Cool Whip with food colouring; spread onto cupcakes.
CUT each large marshmallow crosswise into 5 pieces with clean kitchen shears. Arrange 5 on top of each cupcake to resemble flower. Place 1 miniature marshmallow in center of each. Sprinkle with coloured sugar. Keep refrigerated.