Just because he has 3 colors does not mean he is all yorkie. I would find it very suspicious if someone met me at a pet store with a dog and "forgot" the papers. There are a lot of people here that are still waiting for papers years after a deal. CKC (Continental Kennel Club) is also notorious for registering the birth (not vouching for pedigree) of mixes and undocumented parentage puppies.
Even though parti-colors are off-standard, it is only the color that is any different. Those breeding parti-colors to try for eventual AKC recognition are being very particular about what traits they are continuing. (Look here to see what a parti-color should look like:
http://www.partiyorkies.com/Parti%20Yorkies.htm)
My best dog of all time had to be spayed because it became very apparent that she was no where near the breed standard -- but what a loving dog! She was the
best but her curly coat, over-size, etc. did not need to be continued in the breed. Her parents probably should not have been bred either. Since I did not buy a dog just for breeding, she was still perfect to us! I hope your tri-color will also be a great pet!