Preheat the oven to 350 degrees F (175 degrees C). Grease and flour two 8-inch or 9-inch round cake pans.

In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a separate large bowl, cream together the butter and granulated sugar until light and fluffy.

Beat in the eggs one at a time, mixing well after each addition.

Alternate between adding the dry ingredients and the milk to the wet ingredients, beginning and ending with the dry ingredients. Blend until just combined – don't overmix!

Divide the batter evenly among 4 bowls.

Color each bowl of batter using the food coloring: one pink, one blue, one purple, and one yellow.

Scoop 1/4 cup of one color batter into the center of one pan. Repeat this process with the other colors, alternating and layering the batter into both pans until all the batter is used. You don't need to be super precise – just drop the batter in and go!

Bake the cakes for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 10-15 minutes before inverting onto a wire rack to cool completely.

In a large bowl, beat together the cream cheese and butter until smooth and fluffy.

Add the powdered sugar, one cup at a time, and mix until fully incorporated.

Stir in the vanilla extract.

Divide the frosting among 4 bowls and color each with the food coloring: one pink, one blue, one purple, and one yellow.

Level the tops of the cakes if needed for a flat stacking surface.

Place one cake layer on a serving plate. Frost the top with an even layer of frosting (you can pick one of the colors you made).

Place the second cake layer on top and frost the entire cake with a thin "crumb coat" of white frosting. Chill in the refrigerator for 30 minutes.

After chilling, frost the cake with another layer of white frosting.

Fill four piping bags (or food storage bags) with the different colored frostings.

Pipe swirls and dollops of colored frosting all over the cake in any design you like!

Decorate the cake with sprinkles and edible glitter.

Press the ice cream cone upside-down into the top center of the cake for a unicorn horn. Add the candy eyes, ears, and horn around the ice cream cone, if using.