code: def set_graylevel(self, frac):
          
          DEBUG_MSG("set_graylevel()", 1, self)
          self.select()
          GraphicsContextBase.set_graylevel(self, frac)
          self._pen.SetColour(self.get_wxcolour(self.get_rgb()))
          self.gfx_ctx.SetPen(self._pen)
          self.unselect()
docs: Set the foreground color.  fg can be a matlab format string, a
          html hex color string, an rgb unit tuple, or a float between 0
          and 1.  In the latter case, grayscale is used.