def to_cterm
      return @value if cterm?
      return Convert.hex_to_xterm(to_standard_hex) if hexadecimal?
      return :NONE if none?

      raise ColorError.new "can't convert \"#{ @value }\" to cterm"
    end
def to_cterm
      return @value if cterm?
      return Convert.hex_to_xterm(to_standard_hex) if hexadecimal?
      return :NONE if none?

      raise ColorError.new "can't convert \"#{ @value }\" to cterm"
    end
Convert the color value to a cterm compatible color

 @return [Fixnum]
   the color as either "NONE" or cterm color

 @api public