Preheat the oven to 350 degrees F. with racks in the middle and upper third. Butter and flour two 8 or 9-inch cake pans.
In a small bowl, whisk the food coloring and cocoa together.
In a large bowl, cream together the Crisco, sugar and eggs. Add the red paste and mix well.
Mix in the buttermilk. Slowly mix in the flour and salt.
In a small bowl, combine the vinegar, vanilla and baking soda. Stir into the cake mixture.
Pour the batter evenly into the two cake pans. Bake for about 30 minutes or until a toothpick inserted comes out clean. Allow the cakes to cool before icing.
While the cake is baking: in a medium saucepan, cook the flour and milk over medium heat until thick, stirring constantly. Remove from the heat and let cool to room temperature.
Beat the mixture with an electric mixer for 2 minutes add the butter, Crisco and sugar and beat for an additional 4 minutes.