Prepare the cake mix according to the package directions.

Divide the batter evenly into 5 bowls (about ¾ cup batter per bowl).

Color each bowl using liquid food coloring to make red, yellow, green, blue, and purple batter. Use 5 drops each of red, green, and blue. Use 8 drops of yellow. For purple, mix 2 parts red to 1 part blue (6 drops red, 3 drops blue)

Spoon small dollops of each color randomly into a greased baking pan. A 2-tablespoon portion scoop helps, but a spoon works too.

Gently swirl the colors together using a knife.

Bake according to the cake mix package directions. If using a glass pan, bake at 325°F and check for doneness.

Let the cake cool for 10 minutes.

Use the handle of a wooden spoon to poke holes all over the warm cake.

Whisk together the pudding mix and milk until smooth.

Slowly pour the pudding over the cake, filling the holes as evenly as possible.

Cover and refrigerate for at least 1 hour.

Spread whipped topping over the chilled cake and finish with rainbow sprinkles.

Slice and serve. Store leftovers covered in the refrigerator for up to 3 days.