Preheat the oven to 325 degrees . Line a 12-cup muffin pan with baking liners. In a medium bowl, whisk the oil, buttermilk, egg, food color and vanilla. In another medium bowl, whisk the flour, sugar, cocoa and salt. Add the dry ingredients to the wet ingredients; stir to blend. Divide among muffin cups. Bake until a toothpick inserted into the center comes out clean, about 30 minutes. Let cool.