Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.

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

In another bowl, cream the softened butter and granulated sugar until light and fluffy. This usually takes about 4-5 minutes.

Add in the vanilla extract and eggs one at a time, mixing well after each addition.

Gradually alternate between adding the dry mixture and milk to the wet ingredients, mixing until just combined. Do not overmix!

Divide the batter equally into smaller bowls. Add a few drops of gel food coloring to each bowl, mixing until you achieve your desired colors.

Pour dollops of colored batter into the prepared pans, alternating the colors until all are used.

Place in the preheated oven and bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes before transferring them to wire racks to cool completely.

Once cooled, frost with buttercream frosting, creating a watercolor effect using a palette knife or spatula.