Preheat oven to 350 degrees F. Lightly oil and flour 3 (9 by 1 1/2-inch round) cake pans. In a large bowl, sift together flour, sugar, baking soda, salt, and cocoa powder. In another large bowl, whisk together the oil, buttermilk, egs, food clolring, vinegar, and vanilla. Using a standing mixer, mix the dry ingredients into the wet ingredients until just combined and a smooth batter is formed. Divide the cake evenly among the prepared cake pans. Place the pans in the oven evenly spaced apart. Ba