code: @Override
      public Color getAtomColor(IAtom atom, Color defaultColor) {
          Color color = defaultColor;
          String symbol = atom.getSymbol().toUpperCase();
          if (atom.getAtomicNumber() != null && ATOM_COLORS_MASSNUM.containsKey(atom.getAtomicNumber())) {
              color = ATOM_COLORS_MASSNUM.get(atom.getAtomicNumber()); // lookup by atomic number.
          } else if (ATOM_COLORS_SYMBOL.containsKey(symbol)) {
              color = ATOM_COLORS_SYMBOL.get(symbol); // lookup by atomic symbol.
          }
  
          return new Color(color.getRed(), color.getGreen(), color.getBlue()); // return atom copy.
      }
docs: Returns the font color for atom given atom.
  
  @param atom            the atom.
  @param defaultColor atom default color.
  @return A color for the atom.  The default colour is used if none is
  found for the atom.