docs: def validate_cmap(val):
      """Validate a colormap
  
      Parameters
      ----------
      val: str or :class:`mpl.colors.Colormap`
  
      Returns
      -------
      str or :class:`mpl.colors.Colormap`
  
      Raises
      ------
      ValueError"""
      from matplotlib.colors import Colormap
      try:
          return validate_str(val)
      except ValueError:
          if not isinstance(val, Colormap):
              raise ValueError(
                  "Could not find a valid colormap!")
          return val