In a large mixing bowl, cream sugar and shortening. Add eggs one at a time, beating well after each addition. Beat in food coloring, vinegar, butter flavoring and vanilla. Combine flour, cocoa, baking soda and salt; add to creamed mixture alternately with buttermilk. Pour into three greased and floured 9-inch round baking pans. Bake at 350 F. for 25 to 30 minutes or until toothpick inserted near the center comes out clean. Cool for 10 minutes before removing pans to wire racks to cool completely. In a large mixing bowl, combine frosting ingredients; beat until smooth and creamy. Spread between layers and over top and sides of cake.