Heat oven to 350°F (180°C). Grease and flour or spray with non-stick cooking spray a 12-cup (3 L) fluted tube cake pan. Make cake batter as directed on box. Pour about 2 cups (500 mL) batter into pan. Into small bowl, pour about 3/4 cup (175 mL) batter; stir in food colour and peppermint extract. Carefully pour pink batter over white batter in pan. Carefully pour remaining white batter over pink batter.