Preheat oven to 350°F. Line 2 cupcake pans with cupcake liners.
In a small bowl, sift the cake flour and the salt and set aside.
In a large bowl, on the medium speed of an electric mixer fitted with the paddle attachment, cream the butter and sugar until very light and fluffy, about 5 minutes.
Add the eggs, one at a time, beating well after each addition.
In a small bowl, whisk together the red coloring, cocoa, and vanilla. Add to the batter and beat well.
Add the buttermilk to the batter in three parts alternating with the flour. With each addition, beat on medium-low until the ingredients are incorporated.
In a small bowl, stir together the cider vinegar and baking soda. Add to the batter and mix well. Using a rubber spatula, scrape down the batter in the bowl, making sure the ingredients are well blended and the batter is smooth.
Divide the batter among the prepared cupcake pans. I like to use an ice cream scoop.
Bake for 17-20 minutes. Cupcake is done when the top springs back after touching with your finger (be careful!) or an inserted toothpick is removed with a few crumbs.
Cool cupcakes in pan 10 minutes, then remove from pan and cool completely before icing.