We have 7-month old Boer mix twin sisters. One of the has the typical brown/white Boer markings, the other one is completely white, or at least she was until recently. Over the past 4 weeks we noticed a partial darkening (turning brownish) of her formerly white coat, mostly around one eye, the bridge of her nose, over her shoulders and along her left side. Could this be because she is maturing, and perhaps simply just starting to look more like a Boer, or could this be a copper deficiency (which I have heard will also cause certain color changes)? My goats get alfalfa/orchard hay, free-choice loose goat minerals, and dumor goat chow.