In another bowl and using an electric mixer on medium speed, cream the butter, sugar and colouring mixture until light and fluffy. Add the eggs one at a time, beating until smooth. With the mixer on low speed, add the dry ingredients, alternating with the buttermilk. Divide the batter between the pans. Bake until a toothpick inserted in the centre comes out clean, about 40 minutes. Let cool slightly, then remove from the pans. Let cool to room temperature.