In a small saucepan, combine sugar, flour, cinnamon and salt. Gradually mix in water; add butter. Bring to a boil over high heat and cook for 1 minute. Remove from heat; add vanilla. If desired, add enough food coloring to turn the mixture a deep pink. Let cool. For dumplings, combine flour, sugar, baking powder and salt in a medium bowl. Cut in butter until mixture resembles small peas. Add milk and mix quickly but do not overmix. Shape dough into a ball. On a floured surface, roll dough to a 12-in. x 10-in. rectangle. Spread dough with butter and arrange rhubarb on top. Sprinkle sugar and cinnamon over all. Roll up, jelly-roll style, starting at a long end. Cut into 12 slices. Arrange, cut side up, in a greased 3-qt. baking dish. Pour sauce over dumplings. Bake at 350° for 35 minutes or until dumplings are puffy and golden brown. Serve warm with cream if desired.