Pour lemon juice and water into a small saucepan. Sprinkle gelatin over juice mixture; let set 5 minutes.
Add sugar; bring to a simmer over medium heat, stirring constantly. Remove from heat; stir in lemon peel, corn syrup, and food coloring, if desired.
Chill until slightly thickened, about 45 minutes, or until consistency of pudding, stirring occasionally. Fold whipped topping into gelatin mixture. Pour into pie crust. Chill until served.
POMEGRANATE CHIFFON PIE: Replace lemon juice and water with 1 cup pomegranate juice. Omit food coloring.
ORANGE CHIFFON PIE: Replace lemon juice and water with 1 cup orange juice. Replace lemon peel with orange peel. Add 1 drop red food coloring, if desired.