private String isWinning() {
		int whiteMaterialCount = 0;
		int blackMaterialCount = 0;
		for(int i = 0; i < justRemoved.size(); i++) {
			GameObj temp = justRemoved.get(i);
			if(temp == null) {
				//do nothing
			} else if(temp.isTile()) {
				//do nothing
				//should never reach here
			} else if(temp.getColor().equals(WHITE)) {
				whiteMaterialCount += temp.getMaterialCount();
			} else {
				blackMaterialCount += temp.getMaterialCount();
			}
		}
		if(whiteMaterialCount == blackMaterialCount) {
			return null;
		} else if(whiteMaterialCount < blackMaterialCount) {
			return colorToString(WHITE);
		} else {
			return colorToString(BLACK);
		}
	}