code: public void setColorBackgroundWeekNumberLabels(Color colorBackgroundWeekNumberLabels,
          boolean applyMatchingDefaultBorders) {
          this.colorBackgroundWeekNumberLabels = colorBackgroundWeekNumberLabels;
          if (applyMatchingDefaultBorders) {
              setBorderPropertiesList(null);
          }
          zDrawIndependentCalendarPanelIfNeeded();
      }
docs: setColorBackgroundWeekNumberLabels, This sets the calendar background color for the week
  number labels. The default color is a medium sky blue.
  
  @param applyMatchingDefaultBorders This determines if this function will update the border
  label properties to show the appropriate default borders. The default border label settings
  are different, depending on the "colorBackgroundWeekNumberLabels". If you have not customized
  the border label properties, then it is recommended that you always set the
  "applyMatchingDefaultBorders" parameter to true. This will ensure that the calendar borders
  will always use the correct default settings. If you set this parameter to false, than the
  current border settings will not be changed by this function.