code: protected BufferedImage create_BACKGROUND_Image(final int WIDTH, final String TITLE, final String UNIT_STRING) {
          return create_BACKGROUND_Image(WIDTH, TITLE, UNIT_STRING, null);
      }
docs: Returns the background image with the currently active backgroundcolor
  with the given width, title and unitstring.
  @param WIDTH
  @param TITLE
  @param UNIT_STRING
  @return buffered image containing the background with the selected background design