Preheat oven to 350°F. Spray three 8-inch cake pans with baking nonstick spray. Line the bottoms of the cake pans with 8-inch parchment paper circles. Spray again.
In a medium bowl, sift the flour. Add in the baking powder, baking soda, and salt. Set aside.
3 ½ cups All-purpose flour, 2 teaspoon Baking powder, 1 teaspoon Salt, ¾ teaspoon Baking soda
Using a mixer, beat the butter, oil, and sugar on high speed for 3 minutes. It will be very fluffy. Scrape the bowl. Add in vanilla and sour cream and beat on medium until combined.
¾ cup Unsalted butter, ¼ cup Oil, 1 ½ cups White granulated sugar, ¼ cup Sour cream, 1 tablespoon Clear imitation vanilla
Add in the eggs one at a time and beat on high for 2 minutes. Scrape the bowl.
4 Large eggs
Add in ⅓rd of the dry ingredients and half of the buttermilk. Mix on low. Add in another ⅓rd of the dry ingredients and the rest of the buttermilk. Finish with the rest of the dry ingredients.
1 cup Buttermilk
Pour the cake batter into the three cake pans. Use all of your food dyes and spread 2 drops per dye around the cake evenly. Use a butter knife to swirl the colors together.
Food dye coloring
Bake the cake for 18-23 minutes. Bake until a toothpick inserted comes out clean. Let the cakes sit in the hot pans for 10 minutes before transferring to a cooling rack. Cool the cakes completely.