Preheat oven to 325 degrees F. In large mixer bowl, beat egg yolks with sweetened condensed milk, ReaLime(R) and food coloring if desired. Pour into pastry shell or crumb crust. Bake 30 minutes or until set. Remove from oven. Cool. Chill.
Top with whipped cream. Refrigerate leftovers. Optional: Top with lime slices or zest for added color and decoration.