code: public void setColor(DateArea area, Color color) {
          // If null was supplied, then use the default color.
          if (color == null) {
              color = area.defaultColor;
          }
          // Save the color to the color map.
          colors.put(area, color);
          // Call any "updating functions" that are appropriate for the specified area.
          switch (area) {
              case BackgroundMonthAndYearMenuLabels:
              case BackgroundTodayLabel:
              case BackgroundClearLabel:
                  if (parentCalendarPanel != null) {
                      parentCalendarPanel.zSetAllLabelIndicatorColorsToDefaultState();
                  }
                  break;
              default:
                  if (parentDatePicker != null) {
                      parentDatePicker.zDrawTextFieldIndicators();
                  }
                  zDrawIndependentCalendarPanelIfNeeded();
          }
      }
docs: setColor, This sets a color for the specified area. Setting an area to null will restore the
  default color for that area.