Preheat your oven to 350°F (175°C).
Grease and flour two 9-inch round cake pans or line them with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a large bowl, beat the sugar and oil together until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Mix in the vanilla extract and purple food coloring.
Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk, beginning and ending with the dry ingredients.
Stir in the vinegar.
Divide the batter evenly between the prepared pans.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for about 10 minutes, then transfer to a wire rack to cool completely.