Soak gelatin in water.In double boiler over gently simmering water, beat yolks;add 1/2 cup sugar and lemon juice.Cook, stirring until mixture coats the bottom of a spoon.Add grated lemon peel, gelatin and food coloring.Stir well.Cool in refrigerator about 1/2 hour until slightly thickened.Beat egg whites with 1/2 cup sugar;fold into lemon mixture.Fold in whipped topping.Spoon into baked pie crust.Refrigerate 2 to 3 hours before serving. Garnish with chocolate shavings and lemon slices.