This is quoted from the YTCA site:
http://www.ytca.org/faq.html#B An Important Note About Color in Yorkshire Terriers
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The most distinctive characteristic of an adult Yorkshire Terrier is its long blue and tan silk coat. A puppy is born black and tan, but the only recognized colors for adults when registering with AKC are blue and gold, blue and tan, black and gold, or black and tan.
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The AKC Breed Standard and YTCA Code of Ethics do not recognize any
other color dogs than noted above. This includes all gold, born blue, liver
(also known as red or chocolate), and parti-colors. One of the reasons for
avoiding breeding "off-colored" Yorkies is because it could be a genetic defect that may affect the dog's health. Some health problems can include, but aren't limited to, severe skin problems, allergies, total hair loss and in some cases long-term illness and/or death.
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A responsible breeder will not intentionally breed for undesirable traits.
On very rare occasions, a breeder will have a puppy born with a color anomaly.
That puppy should undergo careful health screenings before being placed in a spay/neuter (non-breeding) home. A breeder should certainly never
promote these deviations as being desirable or rare.
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There are many issues that potential Yorkie owners need to study before
purchasing their dog. We hope you will read the helpful information at this
website and make an informed decision. It could very possibly save you
aggravation, disappointment and expense. We wish you the best of luck
in your pursuit of a happy, healthyYorkshire Terrier. "
This, along with only 4 color combination codes listed on the AKC site are what led me to believe the AKC only registered the Blue/Black/Gold/Tan combinations. If they are making exceptions now, it would be interesting to know how they determine when and how to make them. Are any and all color combinations accepted? I am just curious.