Sprinkle the gelatin on the cold water in the top part of a double boiler. Add the salt and egg yolks; mix well.
Place over boiling water and cook, stirring constantly, for three to five minutes, until the mixture thickens slightly and the gelatin dissolves.
Remove from the heat. Add the fruit-juice concentrate and chill, stirring occasionally, until the mixture mounds slightly when dropped from a spoon.
Beat the egg whites until stiff but not dry. Gradually add the sugar and beat until very stiff. Fold in the gelatin mixture; fold in the whipped cream. Turn into the baked pie shell and chill until firm. If desired, garnish with additional whipped cream and fresh mint.