I just ran across this forum and even though it is old I thought I would answer anyway since this is the number one question I am always asked.
I am a breeder of Silkies and past breeder of Yorkies. I am not saying Silkies are better so please don't think I am slamming Yorkies. I love them but a Silky just happens to be a better fit for me and my family.
Also to answer a couple of the replys.
Silkies just like Yorkies are born black and tan. They gradually turn.
Silkies do not have coarse hair. It is just like their name implies, "Silky".
You can see tons of pictures of my Silkies and info about Silkies at my web site.
http://silkies4u.com Developed around the turn of the century in Australia from crossings of native Australian Terriers and imported Yorkshire Terriers, the Silky Terrier encompasses many of the best qualities of both breeds. The breed was formed when a number of Yorkshire Terriers from England were brought into the Australian states of Victoria and New South Wales at the end of the 1800s.. Originally known as the Sydney Silky, the Silky Terrier is a breed that was developed in the Sydney area of New South Wales, and was first shown in 1907. Some think he owes his existence also to the crossbreeding of Skye and Yorkshire terries, along with the Yorkshire and Australian terriers. His name was changed to the Australian Silky Terrier in the 1950s though today is usually just called Silky Terrier. Yorkie puppies are prone to hypoglycemia (diagnosed by listless behavior and shakiness). Silkies aren't because they aren't as small.
Silkies tend to be easier to house train and not as yippy but, still make excellent watchdogs and alert you when visitors arrive. Silkies do not shed and do not mat as easily as a Yorkie. Regular grooming with a brush and comb is required a couple of times a week.
Yorkies do not shed but, they do mat much easier than the Silky Terrier. The Yorkshire Terrier requires intensive brushing and combing on a daily basis.
The Yorkshire Terrier has a very long, straight, silky coat which is golden-brown at the head, chest, and legs and a distinctive steele grey from the base of the neck to the tip of the tail. The Yorkie is only supposed to be a 'slate' color of blue and the coat is usually heavier and floor length (when kept in show condition).
The Silky Terrier has a long, smooth, silky, and shiny coat. The coat can be any shade of blue from a light steele blue, to pigeon blue, to a darker slate blue, and many shades in between. The tans should be rich and vibrant. Steele blue is the most prized color. The most common color is light silver to dark blue-grey with brown.
The Silky Terrier body has strength and muscle and weighs between 7-10 pounds. They seem smaller than their weight sounds because they are of a sturdier build and are great for children (their bones are stronger than Yorkshire Terriers').
The Yorkie has an approximate weight of 4 -7 pounds (not to exceed 7 lbs though). The Yorkshire Terrier is tolerant of older children, provided they respect its personal space. Due to its small size and bold temperament the Yorkshire Terrier is not recommended for young children unless carefully supervised.
The Silky Terrier has a wedge shape to the head (longer muzzle and flater skull) with ears that stand erect on top of the head. They are a bit longer in body than tall at the shoulders.
Yorkshire Terriers have a small, flat head, with ‘V’-shaped ears. The ears are erect but may tend to sit on the side a bit. They usually have a larger base than the Silky ear. The Yorkie is a square dog meaning that it is as long as it is tall.
The weights listed are show standards only. Yorkies and Silkies both can be larger or smaller.