code: def callback(index, *args):
      """Change a block to red if color is unset, and back to the actor color if set."""
      if mapper.block_attr[index].color is None:
          mapper.block_attr[index].color = "r"
      else:
          mapper.block_attr[index].color = None
  
label_desc: Use image node_id 2 for calling a global function with example usage: callback(index) without return types