code: private void paintBackground(SynthContext ctx, Graphics g, int x, int y, int w, int h, AffineTransform transform) {
          // if the background color of the component is 100% transparent
          // then we should not paint any background graphics. This is a solution
          // for there being no way of turning off Nimbus background painting as
          // basic components are all non-opaque by default.
          Component c  = ctx.getComponent();
          Color     bg = (c != null) ? c.getBackground() : null;
  
          if (bg == null || bg.getAlpha() > 0) {
              SeaGlassPainter backgroundPainter = style.getBackgroundPainter(ctx);
  
              if (backgroundPainter != null) {
                  paint(backgroundPainter, ctx, g, x, y, w, h, transform);
              }
          }
      }
docs: Paint the object's background.
  
  @param ctx       the SynthContext.
  @param g         the Graphics context.
  @param x         the x location corresponding to the upper-left
  coordinate to paint.
  @param y         the y location corresponding to the upper left
  coordinate to paint.
  @param w         the width to paint.
  @param h         the height to paint.
  @param transform the affine transform to apply, or {@code null} if none
  is to be applied.