Pre-heat your oven to 350°F. Grease and flour two 9 inch round cake pans.
In a medium sized bowl, whisk together flour, baking powder and salt. Set aside.
In the bowl of a stand mixer, beat together butter, vegetable oil and sugar until creamy.
Add the eggs to the butter mixture, one at a time, beating well after each addition.
Stir in the vanilla extract.
Alternate adding the dry ingredients and the buttermilk in several additions, stirring until just combined after each addition (1/3 flour, 1/2 milk, 1/3 flour, 1/2 milk, 1/3 flour).
Divide the batter in half. Tint each half with a different colour of food colouring and then pour into the prepared cake pans.
Bake for 30-35 minutes, or until a toothpick inserted into the centre comes out clean.
Allow the cakes to cool in their pans for about 10 minutes, before flipping onto a wire rack to cool completely.