Preheat oven to 350 degrees and place rack in center of oven.
In a standing mixer, beat butter a few seconds on low speed, then gradually add sugar. Increase speed to medium-high and beat 3 to 4 minutes until light-colored and fluffy. Beat in eggs and vanilla until well-combined. Add food coloring and beat until combined.
Whisk together cake flour, cocoa and salt in small bowl. Alternating with the buttermilk, add dry ingredients to creamed mixture at low speed, starting and ending with dry ingredients.
Dissolve soda in vinegar -- it will bubble -- then add and beat on low until combined.
Fill 12 to 15 cupcake liners with batter just short of the rim. Bake 22 to 25 minutes, or until tops feel just firm. Remove from muffin pan and let cool on a wire rack. Frost when cool.