Preheat oven to 350o. Mix condensed milk, egg yolks, and lime juice well. Beat 1 egg white and fold into lime mixture. Add green food coloring to get desired color. Pour into pie shell. Beat remaining egg whites stiff, adding sugar and cream of tartar. Spread meringue on top of lime mixture, spreading to edge of crust. Make a few peaks. Bake until meringue is nicely browned (about 10-15 minutes).