Are you sure it is not more of a black changing into tan/gold change? The face starts out mostly dark with the tan/gold markings. Then it changes to the entire face being tan/gold. It is normal during the puppy months to see lots of entermingled black and gold as the changes happen. There is a great sticky here about Coats, color, etc. that helps explain it better:
http://www.yorkietalk.com/forums/showthread.php?t=16045