Combine gelatin, 3/4 cup sugar, and salt in a large saucepan. Beat egg yolks, lime juice, and water together; stir into gelatin mixture. Cook over low heat, stirring constantly, until mixture comes to a boil. Remove from heat; stir in lime rind and food coloring. Chill, stirring occasionally, until mixture begins to thicken.
Beat egg whites (at room temperature) until foamy. Gradually add 3/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Fold into chilled gelatin mixture. Fold in 3/4 cup whipped cream.
Pour mixture into piecrusts. Chill until firm. Garnish with 3/4 cup whipped cream before serving.