indexed colors used by XTerm

 This subclass of Convert::Color::RGB8 provides lookup of the colors that
 xterm uses by default. Note that the module is not intelligent enough to
 actually parse the XTerm configuration on a machine, nor to query a running
 terminal for its actual colors. It simply implements the colors that are
 present as defaults in the XTerm source code.
 .
 It implements the complete 256-color model in XTerm. This range consists of: