No yorkie of any color but the two recognized Standard colors can be registered unless lying about their color. Obedience and Agility are totally different types of shows. There are good reasons NOT to breed these other colors of Yorkies. One being their genes may not be the best ie: sicklier.
My yorkie was house trained at about 10 weeks. This was with no crate training. She slept by my neck and woke me up to go outside as she wouldn't just down off the bed. A good breeding means an excellent dog. Not from someone who buys a female and a male and breeds them with no investigation into their pedigrees and health records. Only reputable breeders take careful condiseration of both the female and the male they are breeding. They will also take back (and pay back) any Yorkie that doesn't work out for any reason.