Place a sheet of waxed paper on the kitchen counter.
Place the butter and 32 of the marshmallows in a 3-quart saucepan. Heat over low heat, stirring constantly, until the mixture is smooth. Remove the saucepan from the heat.
Stir in the food color and vanilla until the mixture is evenly colored. Stir in the cereal until it is evenly coated.
Lightly spray your hands with cooking spray. For each ball, shape about 1/2 cup cereal mixture into a ball around 1 of the remaining marshmallows. Press the gumdrop pieces into the balls to decorate. Cool completely, about 1 hour. Store the balls in a loosely covered container.