Mix cake flour, cocoa powder, baking soda, and salt in a bowl. Set aside.
In a large bowl, mix vanilla, buttermilk, eggs, and oil until combined.
Add sugar and mix well.
Stir in vinegar and food coloring.
Add dry ingredients and mix until just combined.
Pour in hot water and mix until smooth.
Divide batter into 3 greased and floured 8-inch cake pans.
Bake at 350°F for about 30-40 minutes, or until a toothpick comes out clean.
Let cool before frosting.