Preheat the oven to 350℉ and prepare a 9×13 inch baking pan with a light coating of cooking spray. Set aside.
In a large bowl, combine cake mix, water, vegetable oil, and eggs. Mix until thoroughly combined.
15.25 oz White Cake Mix, 1 cup water, ½ cup oil, 3 egg
Pour batter into the prepared baking pan and bake for 25 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool, then using the handle of a wooden spoon poke holes over each inch of the cake. Set aside.
In three small bowls, combine each gelatin package with 1 cup boiling water. Whisk together until fully combined.
4 cup boiling water, 3 oz strawberry gelatin mix, 3 oz grape gelatin mix, 3 oz blue raspberry gelatin
Use a Tablespoon to pour gelatin mixture into the holes in cake, alternating colors according to preference until each hole has been filled. Do not use all the gelatin.
Place the cake into the refrigerator and let it cool for 2 hours.
If desired, color the whipped topping and spread over the cooled cake and top with sprinkles before serving.
8 oz whipped topping, food coloring, rainbow sprinkles
Notes
You will have lots of gelatin leftover, so be sure to prepare a glass pan for some jelly jigglers!