In a small bowl, mix graham cracker crumbs with melted butter until the texture resembles wet sand. Divide evenly among serving cups, pressing down to create a crust layer.
In a mixing bowl, whisk together the pistachio pudding mix and cold milk for about 2 minutes until thickened.
Gently fold in the whipped topping until fully combined. If you want a deeper green color, add a few drops of green food coloring and mix well.
Spoon or pipe the mousse over the graham cracker crust in each cup, smoothing the top.
Refrigerate for at least 1 hour to allow the mousse to set.
Before serving, top each mousse cup with whipped cream and a sprinkle of chopped pistachios.