Heat oven to 350. Grease and flour two 9" cake pans. Cream shortening and sugar. Add eggs and continue beating hard. Make a paste of food coloring and cocoa, add to mixture and continue to beat hard. Add salt and flour alternately with buttermilk. Add vanilla and beat hard. Add vinegar to soda, then Blend into mixture (don't beat). Pour into greased and floured cake pans and bake 20 - 30 minutes.