Preheat oven to 350F. Grease twelve 2½-inch muffin cups. In a medium bowl, combine flours, baking powder, baking soda and ½ teaspoon salt. Set aside.
In large bowl, combine vegetable oil spread and sugar blend. Beat with electric mixer on medium speed about 3 minutes or until fluffy. Add eggs, buttermilk and the water, beating until well mixed. Add flour mixture, beating on low speed just until blended, being careful not to overmix. Divide batter between two bowls. Stir vanilla into one bowl of the batter. Stir melted chocolate into the other bowl of the batter.
Spoon vanilla batter into one side of each of the prepared muffin cups. Spoon chocolate batter into the other side of each muffin cup, filling the cups two-thirds full. If desired, sprinkle semisweet chocolate pieces over the vanilla batter and white baking pieces over the chocolate batter. Fill any empty cups with water to prevent warping while baking.
Bake for 15 to 17 minutes or until a toothpick inserted in centers comes out clean. Cool in muffin cups on a wire rack for 5 minutes. Remove from muffin cups; serve warm.