Is there a such thing as a white and black/grey miniature yorkshire terrier?

No.
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NO!
YT come in ONE correct size & ONLY "blue&tan".
Anything else is WRONG & probably a mutt.

added-SILKYS ARE ************NOT**************** that color either.They too *MUST* BE BLUE&TAN!!!!!!!!
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no there isnt i believe what you are looking for is in fact a silkshire terrier! they are better than yorkies! Silkies are smarter and have those color coats. heres a link http://www.puppyfind.com/breed/?breed_id=100&back=%2Fsearch%2F%3Fsubmit%3D1%26str%3Dsilky%26page%3D1
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own 2! coat varies heres one of my silkies she is the last one on the page http://kingdompups.bravehost.com/siresandams.html

No, never seen one or heard of one.
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No, white is not an accepted color in the breed. You can get complete information on what is acceptable at the AKC or UKC websites.
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Responsible pet owner 30+ years

No
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Yorkies are toy group dogs…no such thing as a miniature toy breed. Their standard does not allow for a deviation in color. However, the Silky, also a member of the toy group, looks a lot like a Yorkie but with a lighter pallet and those silvery (is that what you mean by black/grey?) colorings. They're about the same size though so the "miniature" is what concerns me and would mean one of two things to me…either you're dealing with a scam artist who mixed breeds to come up with something on his own and try to push it off as legit or you're dealing with someone who knows nothing at all about the breed he is offering for sale…either way, probably not the best person to buy from!
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profressional trainer and animal behaviorist