Cream shortening and sugar. Add eggs and vanilla. Beat well. In a separate dish, blend cocoa and food coloring; add to sugar mixture. Add flour, buttermilk, and salt alternately. Mix soda and vinegar in cup and add. Bake in two 9-in cake pans, greased and floured, at 350 for 30 to 35 minutes. If desired, divide batter between three 9-in pans. Let cool before frosting.