In my opinion, I think multi colored yorkies would be so cute.
I'm not a breeder but do own a standard Black/Gold Yorkie with some blue on the back of his coat.
I think the important thing is to consider any health issues with cross breeding.
I love the standard Yorkie's personality and wouldn't want this to change during cross breeding.
I'm studying Vet Tech. medincine and have seen... Yorkiepoos, Yorki/maltese alot and yes ,they may be cute as a button, but the Maltese mixed with the Yorkie only hightens the chances of Livershunt and other simular diseases.
Gum disease, colapsed trachea...things like this...
I don't think its wise to take 2 different breeds with the same health issues and mix them together.
JMO
Kat