All of ours are full Yorkie and if you watch my avatar it scrolls through the pictures of them....all different colors.
With Houston and Meadow, if we grow them out they are silver/gray, but really blondish when short.
Piper is just crazy blonde coloring and silver under it...we have never quite figured out how she got that coloring....black and tan when she was born...then a trip to the groomers one day and Whamo! Under the black was all this blonde.
She's still a little diva though.