double hGap = plotArea.getWidth() * this.interiorGap;
            double vGap = plotArea.getHeight() * this.interiorGap;
        
            double igx1 = plotArea.getX() + hGap;
            double igx2 = plotArea.getMaxX() - hGap;
            double igy1 = plotArea.getY() + vGap;
            double igy2 = plotArea.getMaxY() - vGap;
            g2.setPaint(Color.gray);
            g2.draw(new Rectangle2D.Double(igx1, igy1, igx2 - igx1, 
                    igy2 - igy1));