1. Sprinkle gelatin over 1/2 cup cold water in a medium bowl. Let stand 2 minutes. Pour 1/2 cup boiling water over gelatin mixture, and stir until gelatin dissolves.
2. Slowly whisk in sweetened condensed milk and next 2 ingredients. Fold in pineapple. Stir in green food coloring, if desired. Pour mixture into a 4-cup ring mold, and chill 4 hours or until set. Gently run a small knife around outer edge of mold to break seal. Dip bottom of mold in warm water for about 15 seconds. Unmold salad onto a serving plate.
3. Beat marshmallow crème and cream cheese at high speed with an electric mixer until stiff peaks form. Stir in 1/4 to 1/2 cup yogurt. Serve with gelatin salad.