Beat together the butter and icing sugar in a bowl until smooth and creamy. Beat in the food colouring. Place in a piping bag fitted with a writing nozzle, or use a paper piping bag with the merest tip snipped off (see
Roll out the green icing on a work surface lightly dusted with icing sugar. Roll very thin ropes of white icing and position them about 5 mm (¼ inch) apart over the green icing. Gently roll with a rolling pin so that the ropes are flattened into the green icing to create a striped effect. Cut out little semicircular shapes and secure one to each cake to resemble a headscarf, using a little piped red buttercream to secure in place. Use the icing trimmings to shape knots on one side.
Shape eyes and smiling mouths from white icing and eye patches and pupils from black icing. Use the red buttercream in the bag to pipe wiggly lines for hair and around the mouths. Arrange on a plate, scattered with chocolate coins, if using.