docs: public static String colorToString(int col) {
      final char[] buf = new char[] { '#', 'X', 'X', 'X', 'X', 'X', 'X' };
      for(int i = 6; i > 0; i--) {
        final int v = (col & 0xF);
        buf[i] = (char) ((v < 10) ? ('0' + v) : ('a' + v - 10));
        col >>>= 4;
      }
      return new String(buf);
    }