code: def pixel(self, x, y, size=None, red=0):
          
          if (size is None):
              size = self.sz
          # Have we go to the smallest element?
          if (size <= 3):
              if (_num(x, y) % 2):
                  return (red, 0, 0)
              else:
                  return None
          divisor = size // 3
          n = _num(x // divisor, y // divisor)
          if (n == 5):
              # Middle square further divided
              return self.pixel(x % divisor, y % divisor,
                                divisor, min(red + 25, 255))
          elif (n % 2):
              return (red, 0, 0)
          else:
              return None
docs: Return color for a pixel.
  
          The paremeter size is used to recursively follow down to smaller
          and smaller middle squares (number 5). The paremeter red is used
          to shade from black to red going toward the middle of the figure.