We have 15 2-week old single combed brown leghorns. Their beaks were yellow, but after a couple of days they all have brown/black on them on the part closest to the body. I researched brown leghorns before I ordered them and all pictures of them they looked like their beaks were always yellow. Chickens with black on their beaks are not considered kosher to us orthodox Jews. Any idea if these should turn yellow again at maturity?