code: private void appendStyleColor(final XMLUtil util, final Appendable appendable) throws IOException {
          appendable.append("<style:text-properties");
          util.appendAttribute(appendable, "fo:color", this.negativeValueColor.hexValue());
          appendable.append("/>");
      }
docs: Appends the style color.
  
  @param util       XML util
  @param appendable where to write
  @throws IOException If an I/O error occurs