Preheat oven to 350°F. Line 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 medium bowl, whisk together buttermilk, red coloring, vanilla, and vinegar. Add half to mixing bowl. Mix and then add half of sifted dry mixture into bowl. Mix until almost combined. Then add remaining wet ingredients followed by remaining dry mixture. Mix until just combined.
Divide batter among prepared cupcake liners. Bake for 18-20 minutes until toothpick inserted in center of cupcake comes out clean. Let cool in pan for 5 minutes before removing and allowing to cool completely on rack.