In a saucepan, combine lime juice with sugar; sprinkle with gelatin. Let soften for 1 minute; heat over medium heat, stirring, for 3 minutes or until dissolved. Stir in lime rind and enough drops of green food coloring to tint bright green(color will soften when cream is added). Let cool to room temperature. Whisk in milk; cover and refrigerate for 15 minutes or until slightly thickened. Whip cream; fold into lime mixture. Spoon into parfait glasses; cover and refrigerate for at least 1 hour or up to 24 hours. Garnish with lime slices. Makes 6 servings.