In a double boiler, stir gelatin with 1/4 cup sugar and salt until well mixed.
In a small bowl with wire whisk, beat egg yolks with cold water and lime juice until mixed; stir into gelatin mixture and cook over hot, NOT BOILING, water, stirring constantly, until mixture thickens and coats a spoon.
Remove from heat, stir in 1 teaspoon of grated peel and food coloring; pour into a large bowl and cool to room temperature, stirring occasionally.
Meanwhile, prepare collar for a 1-quart soufflé dish by cutting a piece of 12-inch-wide foil to fit around the soufflé dish and overlap by about 2 inches (it would be about 24 inches long for a 2-quart dish); then fold the foil in half lengthwise; carefully wrap foil strip around the outside of the dish so that the collar stands about 3 inches above rim; fasten the foil collar securely with a piece of cellophane tape.
In a small bowl with mixer at high speed, beat egg whites until soft peaks form; beating at high speed, gradually sprinkle in 1/2 cup sugar; beat until sugar is completely dissolved- whites should stand in stiff peaks; spoon mixture into bowl with lime mixture.
In a small bowl with mixer at medium speed, whip the cream; gently fold with beaten egg whites into lime mixture.
Pour into prepared soufflé dish; chill until firm, at least 3 hours; carefully remove foil collar and garnish with remaining peel.