Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan by greasing or lining with parchment paper.

Mix the boxed white cake mix with eggs, oil, and water as per the instructions on the box until smooth.

Divide the cake batter into 3-4 bowls and add drops of gel food coloring to each, stirring gently to combine.

Spoon colored batters into the baking pan in alternating colors and gently swirl with a butter knife.

Bake in the preheated oven for 28-32 minutes and check for doneness with a toothpick.

Allow the cake to cool for 15-20 minutes, then poke holes evenly throughout using the handle of a wooden spoon.

Whisk the instant vanilla pudding mix with cold milk for about 2 minutes until slightly thickened.

Pour the prepared pudding over the cooled cake, ensuring it seeps into the holes.

Cover the cake and refrigerate for at least 2 hours to allow it to soak in the pudding.

Once chilled, spread a layer of Cool Whip over the top of the cake.

Decorate the top with optional toppings like sprinkles, berries, or candy eggs before serving.