Read the Yorkshire Terrier standard then you will see what is the right coloring of a yorkie and where each color should be
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Yorkies should only be in 1 color but many people breed both darker and lighter colored yorkies but then they are propably not shown and are in the wrong color.
Fido my Yorkie pup on the avatar is for example with color out of standard.
Many yorkies are 2-3 years to take out their adult color, try going through the coat and see if the root is in another color.
The color turns silver before it turns golden.
The true yorkie color is dark steel blue and golden !
American Kennel Club - Yorkshire Terrier