Heat oven to 350°F for shiny metal or glass pan (or 325°F for dark or nonstick pan). Spray bottom only of 13x9 inch pan with baking spray with flour. Make cake mix as directed on the box, using water, oil, 1½ teaspoons of mint extract, and the egg whites. Reserve 1 cup of batter. Stir 3 drops of the green food color into reserved batter; set aside. Pour remaining batter into pan. Drop green batter by generous tablespoonfuls randomly into 12-14 mounds onto batter in pan. Cut through batter with metal spatula or knife with S-shaped curves in one continuous motion. Turn pan ¼ turn; repeat cutting for swirled design. Bake 28 to 33 minutes or until toothpick inserted center comes clean. Run knife around side of pan to loosen cake. Cool completely for about an hour. Carefully spread fudge topping evenly over cake. In medium bowl, stir whipped topping, remaining extract, 9 drops of green food color and yellow food color until blended. Spread whipped topping over fudge. Garnish with candy pieces. Store in refrigerator.