Heat oven to 325℉/165℃.
Spray a 9 inch loaf pan with baking spray. Set aside.
In a medium bowl, whisk flour, baking powder, and baking soda together. Set aside.
In the bowl of a stand mixer fitted with the flat beater, beat butter and sugar until light and fluffy, about 2-3 minutes.
Add eggs and vanilla, beating well after each addition.
Continue beating until light and fluffy, about 2-3 minutes.
Add flour mixture alternately with buttermilk, beginning and ending with flour mixture.
Stir in vinegar.
Spoon half of the batter into a clean bowl.
Add cocoa powder to the half of the cake batter still inside the mixer.
Mix until combined.
Mix in red food dye and vinegar.
Use a 3 Tablespoon scoop to drop batter in a alternating checkerboard pattern in prepared pan.
Use a flat-bladed knife to swirl batters.
Bake for 70 minutes, or until cake tests done.
Cool in pan for 10-15 minutes.
Turn out and finish cooling on wire rack.