In medium bowl, stir 2 cups boiling water into lime gelatin until gelatin is dissolved. In another medium bowl, slowly stir 1 cup of the lime gelatin into lime yogurt. Pour yogurt mixture into 13x9-inch (3-quart) glass baking dish. Refrigerate about 1 hour or until set. Stir 2/3 cup cold water into remaining plain lime gelatin; let stand at room temperature.