code: public static void updateSubregion(SynthContext state, Graphics g, Rectangle bounds) {
          paintRegion(state, g, bounds);
      }
docs: A convenience method that handles painting of the background for
  subregions. All SynthUI's that have subregions should invoke this method,
  than paint the foreground.
  
  @param state  the SynthContext describing the component, region, and
  state.
  @param g      the Graphics context used to paint the subregion.
  @param bounds the bounds to paint in.