[JennyLeroux]

This subject is debatable. There is no true answer as the only way to find out for 100% sure is to DNA test the original Biewers and original partis and that is not possible. Both of the leading Biewer clubs in the States have researched and one club has DNA tested all dogs in the club to find the answer to that question. The conclusions that they came to is below.

Here is what wikipedia says about Parti Yorkies.

Other colors
A two year old silver blue and gold Yorkshire Terrier
The Yorkshire Terrier is a tan dog with a blue saddle.It does have the parti color. The party color coat Is white with black and tiny places with tan. It's very rare to get a a party color yorkie, and if they are found they tend to be very expensive.[15] The breed is defined by its colour, and colours promoted as "rare" may indicate health problems or crossbreeding with other breeds of other colours.[5] The AKC registration form for Yorkshire Terriers allows for four choices: blue and tan, blue and gold, black and tan, black and gold. Colour alone will not affect whether or not a dog is a good companion and pet. Even though off-coloured Yorkshire Terriers are advertised at premium prices, being of an unusual or untypical colour is neither new, desirable, nor exotic.[15]
Until recently, mismarked Yorkshire Terriers could be crossed with Biewer Terriers, a new breed originally from parti coloured Yorkshire Terriers.[16] Although the American Kennel Club will not deny registration of a Yorkshire Terrier on color alone, the Yorkshire Terrier Club of America has a directive that "any solid color or combination of colors other than blue and tan" for adult dogs is a disqualification, and "dogs of solid color, unusual combination of colors, and parti-colors should be disqualified."[8] This means such dogs are not evaluated in the breed ring, and should not be bred for puppy mills.
http://en.wikipedia.org/wiki/Yorkshire_Terrier

Here is what the Biewer Terrier Club of America says about Biewers.
With the introduction of the Biewer to America in 2003, there has been much speculation about its heritage. Mr. and Mrs. Biewer had been raising and showing Yorkies for 20 years, when on January 20th, 1984 the first blue, white and gold Biewer named Schneeflocken von Friedheck was born. This was the start of what is known as the Biewer Terrier Breed.

Mr. Biewer spent 5 years selectively breeding his dogs until he was able to establish and breed true to a standard uniquely the Biewer Breed. The dogs were then registered as Biewer Yorkshire Terrier a la Pom Pon. In 1989 when Mr. Biewer signed the standard for this wonderful new breed, it was that of the Yorkshire Terrier with the coloring being White-Blue-Gold. Mr. Biewer was not a man of many words, so the standard was short and brief.
http://www.biewer-btca.com/biewerhistory.html

Here is what the Biewer Breed of America says about the Biewers origins.
The Biewer Breed started with foundation parents "Darling von Friedheck" and Fru Fru von Friedheck". Both dogs were blue and tan and were world youth winners in 1981 at Dortmund. Their mating brought the first blue, white and gold Biewer, "Schneeflocken von Freidheck", born in January of 1984.
http://biewerbci.org/History.htm