In 1-quart saucepan, place lime juice; sprinkle with gelatin. Let stand 1 minute to soften. Heat over medium heat about 2 minutes, stirring occasionally, until gelatin is dissolved. Remove from heat; cool slightly. Stir in lime peel.
In medium bowl, mix condensed milk and food colors. Stir in lime juice mixture. Using rubber spatula, fold in all but 1/4 cup of the whipped topping. Spread in pie crust, smoothing top. Cover; refrigerate at least 2 hours or until firm.
Before serving, garnish pie with remaining 1/4 cup whipped topping and lime slices.