Here is a link which also explains the history.
http://eastlandkennels.com/history_o...wer_yorkie.htm
In the not too distant past "off color" pups who were born would be killed becuase they were outsdie the show breed standard and the show breeders did not want to keep those colors in the gene pool.
A breeder in Germany with a more open mind thought these tri-colored puppies were beautiful and made a decision to go against the show breeders and breed FOR the off colors. He started the Biewer Club in Germany and the standard he developed does not allow for docked tails so the tails stay long. The colors come from the fact that the yorkshire terrer was oriniginally developed in the 1800s by cross breeding several different terriers of different colors.
So those who are prejudiced against mixed or cross bred dogs today would do well to remember this.