code: protected void paintTabBorder(Graphics g, int tabPlacement, int tabIndex, int x, int y, int w, int h,
                                    boolean isSelected) {
          //super.paintTabBorder(g, tabPlacement, tabIndex, x, y, w, h, isSelected);
          if (isSelected) {
              g.setColor(Color.GRAY);
          }
          else {
              g.setColor(Color.LIGHT_GRAY);
          }
          g.drawRect(x + 1, y + 1, w - 2, h - 2);
      }
docs: this function draws the border around each tab
  note that this function does now draw the background of the tab.
  that is done elsewhere