Separate egg yolks from whites; set whites aside for meringue.
In a bowl beat yolks well with a fork or whisk. Gradually stir in sweetened condensed milk and lime peel. Add lime juice, water, and, if desired, food coloring; mix well. (Mixture will thicken.) Spoon into pastry shell. Bake in a 325° F oven for 30 minutes. Remove from oven. Increase oven temperature to 350° F.
Meanwhile, for meringue, in a mixing bowl combine egg whites, vanilla extract and cream of tartar. Beat with an electric mixer on medium speed about 1 minute or until soft peaks form (tips curl). Gradually add sugar, 1 tablespoon at a time, beating on high speed about 4 minutes more or until mixture forms stiff, glossy peaks and sugar dissolves. Immediately spread meringue over hot pie filling; seal to edge of pastry. Bake in a 350° F oven for 15 minutes; cool 1 hour. Chill to store.Makes 8 Source: