In a 2-qt. microwave-safe dish, combine the fruit, water and tapioca Let stand for 5 minutes. Cover and microwave on high for 3-1/2 minutes. Stir; cook 2-1/2 minutes longer or until the rhubarb is tender. Stir in the sugar. Cover and microwave for 1-2 minutes. Stir in food coloring if desired.