code: public void setCustomBackground(final Paint CUSTOM_BACKGROUND) {
          model.setCustomBackground(CUSTOM_BACKGROUND);
          if (model.getBackgroundColor() == BackgroundColor.CUSTOM) {
              reInitialize();
          }
      }
docs: Sets the custom background paint that will be used instead of
  the predefined backgroundcolors like DARK_GRAY, BEIGE etc.
  @param CUSTOM_BACKGROUND