new_contents: _system_colors = {
      'toolbar-background' : '#414141'
  }
  
  def _html_to_rgb(html_color):
      """ #RRGGBB -> (r, g, b) tuple (in float format) """
  
      html_color = html_color.strip()
      if html_color[0] == '#':
          html_color = html_color[1:]
      if len(html_color) != 6:
          raise ValueError, "input #%s is not in #RRGGBB format" % html_color
  
      r, g, b = html_color[:2], html_color[2:4], html_color[4:]
      r, g, b = [int(n, 16) for n in (r, g, b)]
      r, g, b = (r / 255.0, g / 255.0, b / 255.0)
  
      return (r, g, b)
  
  class Color(object):
      RED   = Color(1.0, 0.0, 0.0)
      GREEN = Color(0.0, 1.0, 0.0)
      BLUE  = Color(0.0, 0.0, 1.0)
  
      def __init__(self, r, g, b, a=1.0):
          self._r = r
          self._g = g
          self._b = b
  
      def to_rgb(self):
          return (self._r, self._g, self._b)
  
  class SystemColor(Color):
      TOOLBAR_BACKGROUND = SystemColor('toolbar-background')
  
      def __init__(self, color_id):
          rgb = _html_to_rgb(_system_colors[color_id])
          Color.__init__(*rgb)
  
subject: Add a color class, not used yet