Sprinkle gelatin over lime juice and let it stand for i minute. Add boiling water and sweetener to gelatin mixture and stir until gelatin is dissolved. Refrigerate about 45 minutes or until slightly thickened. Combine milk and vanilla and freeze 30 minutes. Remove from freezer and whip at high speed until stiff. Stir lime juice and food coloring into whipped milk. (Save remaining 1/2 lime for garnish.) Slowly blend gelatin mixture into whipped milk. Spoon pie filling into crust. Chill until firm. Garnish with lime zest and lime slices. Cut into 8 even portions and serve 1 portion per serving. Nutritive value per serving: 111 calories; 14 gm. cholesterol; 4 gm. protein; 5 gm. fat; 130 mg. sodium Food Exchanges per serving: 1 bread, 1 fat Low-sodium diets: Use salt-free crust