code: public String mapColorNr(String colorNr) {
          if(this.importColorMapping.containsKey(colorNr)) {
              return (String) this.importColorMapping.get(colorNr);
          } else {
              return "0";
          }
      }
docs: Performs the mapping from the original font number to the actual font
  number used in the RTF document. If the color number was not
  seen during import (thus no mapping) then 0 is returned, guaranteeing
  that the color number is always valid.
  
  @param colorNr The color number to map.
  @return The mapped color number