Preheat the oven to 350°F (175°C). Grease the bottoms of two 9x13-inch glass baking dishes.

Mix chocolate cake mix, 1 ¼ cups water, 1/2 cup vegetable oil, and 3 eggs in a large bowl with an electric mixer on medium speed until well combined. Pour into one of the prepared baking dishes.

Mix white cake mix, 1 cup water, 1/2 cup vegetable oil, and 3 egg whites in another large bowl on medium speed with clean beaters until well combined. Pour into the second prepared baking dish.

Bake cakes in the preheated oven until a toothpick inserted in the center comes out clean, about 30 to 35 minutes for the chocolate cake and 29 to 34 minutes for the white cake. Remove from the oven and let cool to room temperature on a wire rack, about 30 minutes.

While the cakes are baking, make the pudding: Whisk cold milk and pudding mix together in a large bowl for 2 minutes. Refrigerate until needed.

Crumble cookies in small batches in a food processor, scraping down the sides of the bowl often. Place 1/4 cup crumbs into a small bowl; stir in food coloring until crumbs are green. Set remaining crumbs aside.

Unwrap candy rolls. Line the kitty litter box with the liner.

Crumble cooled cakes into a large bowl. Add 1/2 of the uncolored cookie crumbs and some chilled pudding; toss to blend, adding more pudding as needed until mixture is moist but not soggy. Pour mixture into the kitty litter box.

Microwave 1/2 of the candy rolls in a microwave-safe dish until soft, 30 to 60 seconds. Shape the ends so they are no longer blunt, then curve the candies slightly. Bury candies randomly in the litter box and sprinkle with 1/2 of the remaining uncolored cookie crumbs. Sprinkle a few green crumbs over top.

Microwave 3 to 4 candies until almost melted. Place them on top of the cake and sprinkle some green crumbs over top.