I believe YTCA base the breed standard to what is really healthy. About colors, it really would be great if yorkies can have a variety of colors like pomeranians, chihuahuas and shih tzu. However, studies prove that off-colored yorkies have health issues which hinder the health improvement aspect of the breed. Partis and biewers often have shorter life spans. Blue born yorkies are prone to alopecia. Chocolates have pigmentation issues. It's really inevitable that some would claim that some breeders (those who really stick with the stardards) would just want to keep the off-colored yorkies away. But it's really for the benefit of the breed and protection of the breed that the standard has been established.
Here are the articles to explain the genetics...
Top Parti Yorkies Genetics Parti Yorkie Parti Color Yorkshire Terrier and Biewer Yorkies Top Yorkie Genetics Chocolate Yorkies Chocolate Yorkie Red Golden Blue Born Yorkshire Terrier
All pure-breds are man made and developed through thorough in-breeding already and the gene pool is already limited. The standard Yorkshire Terrier needs further improvement to minimize the genetic health concerns that manifest in the breed. It is really playing with fire if breeders would already jump into bringing out the recessive genes and mutated coloring genes just to bring out other colors when the standard yorkie with the dominant and accepted coloring of blue/tan (golden tan) already encounters genetic problems.
Let's just hope more advancements in genetics to the point that all the genetic markers of diseases in the dna have been found and hereditary diseases can be identified. Then maybe, in the future, breeders can zero out on true healthy specimens and colors won't be an issue if a dog is proven free of genetic problems.
