Preheat your oven to 350°F (175°C). Grease and flour three 8-inch round cake pans and set them aside.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large bowl, cream the butter and sugar together until light and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk in three additions, beginning and ending with the dry mixture. Mix until just combined.

Divide the batter evenly into six bowls. Add a few drops of gel food coloring to each bowl to create red, orange, yellow, green, blue, and purple batter. Mix each bowl until the color is fully incorporated.

Using a small cookie scoop or spoon, drop small dollops of each colored batter randomly into one of the prepared cake pans. Repeat the process with the other two pans, ensuring the colors are evenly distributed.

Bake the cakes in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

While the cakes are cooling, prepare the whipped cream frosting. In a large bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Once the cakes are completely cool, layer them with whipped cream frosting between each layer. Spread the frosting over the top and sides of the cake for full coverage.

Decorate the cake with sprinkles or edible decorations as desired. Serve and enjoy!