Preheat your oven to the temperature indicated on the box. Grease a 9x13-inch baking dish with baking spray and set it aside. Prepare the cake mix following the instructions on the box.

Once the batter is ready, divide it into four equal portions. Add a few drops of food coloring to each bowl and stir well. Using a spoon, drop small spoonfuls of each colored batter onto the bottom of the baking dish. The drops will spread in the greased dish, so do this quickly. I recommend adding one color at a time, leaving a few inches between each drop. After adding the first color, proceed with the second, third, and fourth colors until the entire bottom of the dish is covered. Then, layer another round of batter on top and continue until all the batter is used. Tap the baking dish gently on the counter to level the surface, but avoid spreading it with a spatula to keep the colors from mixing. Using a toothpick, swirl the colors slightly—be careful not to over-mix; you want to see distinct swirls, not a fully blended batter. Bake as directed on the box.

Once the cake is baked, let it sit at room temperature for about 10 minutes. Then, use the handle end of a wooden spoon to poke holes all over the top of the cake, about an inch apart. Allow the cake to cool completely.

In a bowl, whisk together the white chocolate pudding mix and milk until the pudding is fully dissolved. Before the pudding sets completely, pour it over the cooled cake, ensuring it fills all the holes. Spread the remaining pudding over the top of the cake and place it in the refrigerator to set completely.

When the pudding has set and the cake is fully cooled, prepare the whipped cream. In a chilled bowl, whip the heavy cream and vanilla extract until soft peaks form. Add the powdered sugar and continue whipping until stiff peaks form. Spread the whipped cream over the pudding layer.

Garnish with sprinkles before serving. Store the cake in the refrigerator.