code: protected void plotGray(SVGPlot plot, Element parent, double x, double y, double size) {
      Element marker = plot.svgCircle(x, y, size * .5);
      SVGUtil.setStyle(marker, SVGConstants.CSS_FILL_PROPERTY + ":" + greycolor);
      parent.appendChild(marker);
    }
docs: Plot a replacement marker when an object is to be plotted as "disabled",
  usually gray.
  
  @param plot Plot to draw to
  @param parent Parent element
  @param x X position
  @param y Y position
  @param size Size