1Heat oven to 350°F. Place flour in medium bowl. Cut in butter, using pastry blender (or pulling 2 table knives through flour in opposite directions), until evenly mixed. Stir in walnuts and 1 teaspoon lime peel. Press evenly in bottom of ungreased 9-inch square pan.
2Bake about 15 minutes or until light brown. Cool completely, about 30 minutes.
3In medium bowl, mix condensed milk, lime juice and 2 teaspoons lime peel; set aside. In chilled large bowl, beat whipping cream and food color with electric mixer on high speed until stiff.
4Fold lime mixture into whipped cream just until blended. Pour over crust. Cover; refrigerate at least 2 hours until chilled but no longer than 48 hours. Store covered in refrigerator.