title: Apache POI background color style seems not working
body: <p>Good evening!
  I've some trouble with apache poi v. 3.14, when I open the rendered xlsx with Libreoffice or Excel the style is not applied correctly.</p>
  
  <p>I have this code:</p>
  
  <pre><code>class... {
  
  private XSSFCellStyle doubleLockStyle;
  /**
       * Create default cell style.
       *
       * @param myWorkBook
       * @return The cell style.
       */
      private XSSFCellStyle createCell(XSSFWorkbook myWorkBook, boolean locked) {
          XSSFCellStyle cs = myWorkBook.createCellStyle();
          cs.setAlignment(HorizontalAlignment.CENTER);
          if (locked) {
              cs.setFillBackgroundColor(LOCKED_COLOR); //rgb from awt colors
              cs.setFillPattern(FillPatternType.SOLID_FOREGROUND);
              cs.setLocked(true);
          } else {
              cs.setLocked(false);
          }
          return cs;
      }
  
       /**
       * Prepare cell styles.
       *
       * @param myWorkBook
       */
      private void initStyles(XSSFWorkbook myWorkBook) {
       ...
          short df = myWorkBook.createDataFormat().getFormat("0.00");
          doubleLockStyle = createCell(myWorkBook, true);
          doubleLockStyle.setDataFormat(df);
       ...
      }
      private void writeSheet(XSSFWorkbook myWorkBook, CalendarValueType type, Date startDate, Date endDate) {
       ...
       cell.setCellStyle(doubleLockStyle);
       ... 
      }
  }
  </code></pre>
  
  <p>Sheet is set as locked. 
  The output doesn't show the background colors and doesn't lock the cells. 
  I can't figure out what's the problem. I've also tried to see if it's a knowed bug, but it isn't.
  Anyone have had the same problem?
  The cells locks if i change the background fill pattern to oblique lines, but the background doesn't appar correctly between Excel and Libre office. 
  Thank you!</p>