1 1/2 c. crushed salted pretzels
2 tbsp. sugar
3/4 c. (1 1/2 sticks) melted butter
1 8-oz. pkg. cream cheese, softened
1 14-oz. can sweetened condensed milk
1/2 c. lime juice
Few drops green food coloring, if desired
1 8-oz. container extra creamy Cool Whip
1 sm. container whipped topping for garnish (optional)