How do I know if my puppy is a Yorkie or Morkie?

"rare" = BYB crap.
And there's your answer.
References :

There is NO SUCH THING as a white Yorkie - it's not "rare"; it's impossible. The genes do not exist.

You have a mix; and whomever bred it and registered it as a purebred Yorkie is an unethical, lying twit. Whomever advertised and sold it as "rare" was looking for a gullible sucker. I hope that wasn't you.
References :

What "papers"?? through what registry?

If you spent money purchasing this pup…and found out it wasn't what you thought…would you love it any less?

btw: BIG RED FLAG when someone sells a pup as a "rare" anything…usually indicates a BYB / hobby breeder, and a badly bred mutt.
References :

BYB alert!
References :

What papers? AKC?? (<–even though I doubt it)

If the "papers" are anything but AKC, I would seriously doubt the purebred-ness of your dog.

White purebred yorkies dont exist.
References :

What you've received is a poorly bred mutt from an unreputable backyard greeder, puppy miller or pet store. What papers? Are they from a legit kennel club? Most likely, NOT, probably something like the Continental Kennel Club or other such bogus KC's. There is no such thing as a MORKIE, it's a mutt.
References :

If it's white, it's 100% got a mix in there, likely poodle or maltese.
If you paid a lot money for this dog you should be very upset. The papers (which I am assuming is just a vet record, certificate of birth, etc.) could have been altered or may even be for a different dog (I've seen this before!)
References :

There is no such thing as a white yorkie…do some research. There is also no such breed as a "morkie", it's just short for Maltese/Yorkie MIX. So either way, what you have is a mutt. If you really want to know what breeds are in her then get a DNA test from the vet.

http://www.dummies.com/how-to/content/knowing-what-an-ideal-yorkshire-terrier-looks-like.html

http://www.akc.org/breeds/yorkshire_terrier/index.cfm
References :

ROFLOL - there is no such recognised breed as a Morkie - it's a crossbreed.

"RARE" ? - lmao - that is a backyard breeder scam - morkie is a made=up name and you have probably been ripped off into paying over the odds if you believe you have a "rare" designer dog.

Purebred Yorkies are not white and not within the breed standard. If your dog was a purebred you would have the necessary legitimate AKC registration certificate.
#
References :

There are no "rare white Yorkies." I would think your little one is not a pure Yorkie.
References :

I have a yorkie and she is steel grey and blonde, i have never heard of a white yorkie. But even if it wasn't a real yorkie, would you love it any less?
References :

You can get a DNA test at your Vet. I am sure it is expensive. If you love your dog, does it really matter?
References :