Hi
My Mika is 8 months too and she is still quite black on her back but her roots are silvery/blue. It can take a while for their true colours to come in or so I'm told (Mika is my 1st yorkie) Are you growing her coat out? If you were to get her clipped you may be able to see her true colours now, though yorkies can continue changing throuhout their lives from what I've seen.
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