Preheat oven to 350 degrees F. Line standard 12-cavity muffin pan with cupcake liners. Set aside.
Sift together flour, baking soda, salt, and cocoa powder. Set aside.
In the bowl of a stand mixer, beat together sugar and vegetable oil. Add egg. Mix until combined.
In a separate bowl, whisk together buttermilk, red coloring, vanilla, and vinegar. Add half of liquid mixture to mixing bowl. Mix on low speed. Add half of sifted dry mixture into mixing bowl. Mix until almost combined. Then add remaining wet ingredients followed by remaining dry mixture. Mix until just combined. Scrape down bowl as needed to ensure thorough mixing.
Divide batter among prepared cupcake pan. Bake for 18-20 minutes until toothpick inserted in center of cupcakes comes out clean. Let cool in pan for 5 minutes. Gently remove cupcakes from pan and allow to cool to room temperature on wire racks.