code: public void setHeaderBackgroundColor(String color) throws HelloSignException {
          if (white_labeling_options == null) {
              white_labeling_options = new WhiteLabelingOptions();
          }
          white_labeling_options.setHeaderBackgroundColor(color);
      }
docs: Set the signer page header background color.
  
  @param color String hex color code
  @throws HelloSignException thrown if the color string is an invalid hex
  string