docs: def parse_ctuple(s,length=2):
      '''parse a string of acceptable colors into matplotlib, that is, either
         strings, or three tuples of rgb. Don't quote strings.
      '''
      if parse_utuple(s, colrx_s, length=length) is None:
          raise ValueError("{} is not a valid color tuple.".format(s));
      #quote strings
      s=quote_subs(s,colorfix=True);
      return evalt(s);