1. Combine graham cracker crumbs, sugar and melted butter.
2. Divide the graham cracker crumb mixture evenly among the six jars. Lightly press down to make the crust.
3. Mix cream cheese, sugar, vanilla, key lime juice and key lime zest together in a large bowl until smooth and well combined.
4. Gently stir in Cool Whip and green food color.
5. Pipe, or spoon, cheesecake mixture into the six jars.
6. Top with additional Cool Whip.
7. Garnish with key lime slices and graham cracker crumbs, if desired.
8. Refrigerate for about 5 hours or until firm.