Pour milk into a small metal bowl; place mixer beaters in the bowl. cover and chill for at least 2 hours. In a saucepan, sprinkle gelatin over cold water; let stand for 2 minutes. Stir in sugar; heat until sugar and gelatin are dissolved. Remove from the heat; stir in lemonade concentrate and food coloring if desired. Cover and chill until slightly thickened. Gradually add to chilled milk; beat until light and fluffy. Fold in cake. Pour into an 8x4-in. loaf pan coated with cooking spray. Cover and chill for at least 2 hours. Remove from pan; cut into eight slices.