Meanwhile, beat next 4 ingredients in large bowl with mixer until blended. Add sour cream; mix well. Add eggs, 1 at a time, mixing on low speed after each just until blended. Measure about 1-3/4 cups batter into separate bowl; tint with red food colouring. Measure 1-1/2 cups of the remaining batter into separate bowl; tint with orange food colouring. Continue to divide remaining batter into 4 additional bowls, decreasing measure of batter in each bowl by additional 1/4 cup as you work your way down to the last bowl which should have only about 1/2 cup batter. Tint each of the remaining plain batters with a different colour food colouring, adding in order listed in ingredient list.