In a mixing bowl, combine grapefruit sections and 3/4 cup of the sugar. Set aside. In a small mixing bowl, combine gelatin and 1/2 cup of the cold water. Let stand 5 minutes.
Meanwhile, in a medium saucepan, combine the remaining sugar and remaining cold water. Heat and stir until sugar dissolves. Add gelatin mixture; grapefruit mixture; nuts; and, if desired, food coloring. Cook and stir until sugar is completely dissolved. Pour grapefruit mixture into a 2-quart mold or square baking dish. Cover; chill at least 6 hours. If using mold, unmold salad. Serve with whipped cream, if desired. Garnish with grapefruit peel curls, if desired. Makes 9 servings.