Place ingredients in a food processor. Process until the mixture is smooth. Pour into a non-metal container. Freeze just until firm, about 2 hours. Break up into pieces and process in food processor until smooth. Return grapefruit mixture to container and freeze until firm. Remove from freezer about 10 minutes before serving. Spoon into serving dishes. Makes 6 servings. PER SERVING: Cal. 56(3%DV), Total Fat <1gram(0%DV), Sat. Fat 0grams, Chol 0mg, Sodium 5mg(0%DV), Pot. 89mg(3%DV), Carb. 14grams(5%DV), Dietary Fiber >1mg(3%DV), Total Sugars 3grams, Protein <1gram(0%DV), Vit. A 63 IU(0%DV), Vit. C 23mg(40%DV), Calcium 9mg(0%DV), Iron <1mg(0%DV), Vit. E 0 IU, Zinc <1mg Dietary Exchange: Fruit 1