For the Crust: In a medium bowl, combine chocolate cookie crumbs and melted butter. Press the mixture into the bottom of a 9x13-inch baking dish. Chill in the refrigerator while preparing the other layers.
For the Orange Layer: In a large bowl, beat the softened cream cheese and powdered sugar until smooth. Fold in the whipped topping. Add orange food coloring and mix until evenly colored. Spread the orange layer over the chilled crust.
For the Purple Layer: In a medium bowl, whisk together the vanilla pudding mix and cold milk until thickened. Add purple food coloring and mix until evenly colored. Spread the purple layer over the orange layer.
For the Green Layer: In another medium bowl, whisk together the pistachio pudding mix and cold milk until thickened. Add green food coloring and mix until evenly colored. Spread the green layer over the purple layer.
For the Topping: Spread the remaining whipped topping over the green layer. Refrigerate for at least 2 hours before serving to allow the layers to set. Just prior to serving, decorate the top with Halloween-themed sprinkles. Cut into squares and serve chilled.