code: def mask_color(clip, color=None, threshold=0, stiffness=1):
      """Returns a new clip with a mask for transparency where the original
      clip is of the given color.
  
      You can also have a "progressive" mask by specifying a non-null distance
      threshold ``threshold``. In this case, if the distance between a pixel and
      the given color is d, the transparency will be
  
      d**stiffness / (threshold**stiffness + d**stiffness)
  
      which is 1 when d>>threshold and 0 for d<<threshold, the stiffness of the
      effect being parametrized by ``stiffness``
      """
      if color is None:
          color = [0, 0, 0]
  
      color = np.array(color)
  
      def hill(x):
          if threshold:
              return x**stiffness / (
                  threshold**stiffness + x**stiffness
              )
          else:
              return 1.0 * (x != 0)
  
      def flim(im):
          return hill(np.sqrt(((im - color) ** 2).sum(axis=2)))
  
      mask = clip.image_transform(flim)
      mask.is_mask = True
      new_clip = clip.with_mask(mask)
      return new_clip
  
label_desc: Use image node_id 1 for calling a global function with example usage: mask_color(clip, color, threshold, stiffness) and returns: new_clip, hill, unknown, unknown