Heat oven to 350°. Grease and flour two 9" round baking pans.
In large mixer bowl beat butter, sugar and vanilla until creamy.
Add eggs and food color; blend well. Stir together flour, cocoa and salt; add alternately with buttermilk to batter mixture, beating until well blended.
Stir baking soda into vinegar; fold carefully into batter (do not beat).
Pour batter into prepared pans. Bake 30-35 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pans to wire racks. Cool completely.
Makes 10 to 12 servings.