Cream shortening and sugar; add eggs and blend. Add food coloring, water and cocoa. Blend in buttermilk; add flour and salt gradually. Add vanilla and beat until mixed. Mix vinegar and soda and stir in last; do not beat. Pour into 2 9-inch pans. Bake for 30 to 35 minutes in a 350-degree oven. Frost with Fluff Frosting.
Add milk mixture and vanilla; continue beating. When icing is very fluffy, frost cool cake.