code: def defaultcolour(self, colour):
          
          if colour == None:
              if self.negative == True:
                  if self.pilimage.mode == "L" :
                      return 0
                  else :
                      return (0, 0, 0)
              else :
                  if self.pilimage.mode == "L" :
                      return 255
                  else :
                      return (255, 255, 255)
          else :
              if self.pilimage.mode == "RGB" and type(colour) == type(0):
                  return (colour, colour, colour)
              else :
                  return colour
docs: Auxiliary method to choose a default colour.
          Give me a user provided colour : if it is None, I change it to the default colour, respecting negative.
          Plus, if the image is in RGB mode and you give me 128 for a gray, I translate this to the expected (128, 128, 128) ...