private String change(String pos,char color){
		String res = "";
		char token  = color  == 'R' ?  'B':'R';
		String regex = ".*[A-H]\\d"+color+"((:?[A-H]\\d"+token+")+)"+"[A-H]\\d"+color+".*";
		Pattern p = Pattern.compile(regex);
		Matcher m = p.matcher(pos);
		if(m.matches()){
			res = m.group(1);
		}
		return res;
	}