In small saucepan stir together sugar and gelatin; stir in cold water. Cook and stir over low heat just until gelatin dissolves. Transfer to a large bowl; cool slightly.
Stir egg product, lemonade concentrate, lime peel, lime juice, and, if desired, green food coloring into gelatin mixture. Cover and chill about 40 minutes or just until mixture starts to mound when spooned, stirring occasionally.
Fold whipped topping into gelatin mixture. Cover and chill about 20 minutes more or until mixture mounds when spooned. Transfer filling to crust. Cover loosely and chill for 3 to 4 hours or until firm. Makes 10 servings.
Preheat oven to 350 degrees F. Lightly coat 9-inch pie plate with nonstick cooking spray. In medium bowl combine pretzels, butter, and egg white; toss gently to combine. Press onto bottom and side of prepared pie plate. Bake for 15 minutes. Cool on wire rack.