code: @Override
      public Color getAtomColor(IAtom atom, Color defaultColor) {
          Color color = defaultColor;
          if (atom.getAtomicNumber() == null) return defaultColor;
          int atomnumber = atom.getAtomicNumber();
          switch (atomnumber) {
              case 1:
                  color = HYDROGEN;
                  break;
              case 6:
                  color = CARBON;
                  break;
              case 7:
                  color = NITROGEN;
                  break;
              case 8:
                  color = OXYGEN;
                  break;
              case 15:
                  color = PHOSPHORUS;
                  break;
              case 16:
                  color = SULPHUR;
                  break;
              case 17:
                  color = CHLORINE;
                  break;
          }
          return color;
      }
docs: Returns the CDK scheme color for the given atom's element, or
  defaults to the given color if no color is defined.
  
  @param atom         IAtom to get a color for
  @param defaultColor Color returned if this scheme does not define
  a color for the passed IAtom
  @return             the atom's color according to this coloring scheme.