code: public void setHeaderTheme(String value) {
          headerTheme = value;
          ComplexPanel r = findHeadRow();
          if (r != null) setEltHeaderTheme(r.getElement(), value);
          r = findHeadGroupsRow();
          if (r != null) setEltHeaderTheme(r.getElement(), value);
      }
docs: Swatch header color "ui-bar-" + value will be used