Grapefruit avocado mold

1 lb can (2 cups) grapefruit sections
2 envelopes (2 tbls) unflavored gelatin
1 cup cold water
1/8 tsp salt
2 7-oz bottles lemon-lime carbonated beverage
3 drops green food coloring
1 avocado

1. Drain the grapefruit sections, reserving the syrup. To the syrup, add enough water to make 1 cup of liquid. Soften the gelatin in the syrup liquid and then cook and stir until the gelatin dissolves. Stir in the cold water and salt and chill until cold but not set.
2. Add the lemon-lime beverage and food coloring to the gelatin.
3. Pour about 2/3 cup of the mixture into a lightly oiled 5 1/2 cup ring mold. Peel and thinly slice 1/3 of the avode, arranging the slices in the bottom of the mold. Chill until the gelatin is almost set. Chill the remaining gelatin until it is partially set.
4. Halve the grapefruit sections. Seed and peel the remainder of the avocado and cut into 1/2-inch cubes. Fold the grapefruit and avocado into the partially set gelatin. Pour this into the mold. Chill until firm.
5. To unmold: Loosed the edges with the tip of a spatula. Dip the mold just to the rim in warm water for a few seconds. Tilt the mold slightly to loosed the gelatin. Place a chilled serving plate upside down over the mold. Holding the plate and mold together, invert and lift off the mold. Chill until serving time.