Place the green gelatin powder in a medium mixing bowl.
Add 1 cup boiling water to the gelatin powder, and whisk to combine.
Add the cold water and chilled vodka.
Whisk to combine.
Fill each plastic cup halfway full with Green gelatin.
Place the cups in the fridge and chill until the gelatin is just about set, about 1 hour.
Black Layer
Place the grape gelatin mix powder in a medium mixing bowl.
Add 1 cup boiling water to the gelatin powder and whisk to combine.
Add the cold water and chilled Spiced Rum.
Whisk to combine.
Sit to the side for 30 minutes to reach room temperature.
Remove the gelatin plastic cups from the fridge and carefully pour the black gelatin over the green gelatin.
Return the gelatin cups to the fridge and chill until completely set, at least 1-2 hours