Just keep working on the grooming and give treats for good behavior.
As for changing colors, I have watched three Yorkies grow up....Tyson is five and I swear his hair color is still changing...I'm starting to see some red tones!
And I just wanted to say about Ann's (Wylies Mom) avatar....I don't know which of her dogs that is, but I think it's probably the cutest Yorkie face I've ever seen