The weight of the parents seem healthy, as they should always be over 5lbs for breeding. Both my babies had a white chest. As another mentioned, that usually fades.
The puppy pictures are super cute! Most purebred and yorkie mixes will look like Yorkies as puppies. The 'mix' part doesn't really show until they're older. The only way to know for sure is to know what the parents, grandparents, etc look like. And I agree, the adults coats will change from whatever the puppy coat is.
Congrats on picking your puppy!! Fun (and tiring) times ahead!!
Yay!!