In a large mixing bowl, whisk together the vanilla instant pudding mix and milk until smooth and beginning to thicken.
Add the mint extract and a generous amount of green gel food coloring. Whisk again until the color is evenly mixed and the filling looks a bright minty green.
Add the Cool Whip and fold it in until the mixture is light and fluffy. If you want a deeper green color, mix in a little more gel food coloring until you reach your desired shade.
Spoon the filling into the store bought graham cracker crust and smooth the top evenly with a spatula.
Refrigerate the pie for at least 4 hours, or overnight, until the filling is fully set and slices hold their shape.
Right before serving, top with extra Cool Whip if desired and garnish each slice with a maraschino cherry. Serve chilled.
