1. Preheat oven to 350°. Beat butter at medium speed with an electric mixer until fluffy; gradually add sugar, beating well. Add eggs, 1 at a time, beating until blended after each addition. Stir in food coloring and vanilla until blended.
2. Combine flour, cocoa, and salt. Stir together buttermilk, vinegar, and baking soda in a 4-cup liquid measuring cup. (Mixture will bubble.) Add flour mixture to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Place 24 paper baking cups in 2 (12-cup) muffin pans; spoon batter into cups, filling three-fourths full.
3. Bake at 350° for 18 to 20 minutes or until wooden pick inserted in centers comes out clean. Remove cupcakes from pans to wire racks, and let cool completely (about 45 minutes).
4. Pipe frosting onto cupcakes. Garnish, if desired.