In a mixing bowl, cream sugar and butter.Beat until light and fluffy.Add eggs, one at a time; mix well after each.Mix cocoa and food coloring together.Add to sugar mixture and mix.
Sift flour and salt.Add flour mixture to the creamed mixture alternately with buttermilk.Blend in vanilla.
In small bowl, combine baking soda and vinegar and add to mixture.
Pour batter into three 8-inch-round greased and floured pans.Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.Cool completely before frosting.