Welcome to YT.
I have always had bigger yorkies, my last girl weighed in at 17 pounds, my smallest was 9 pounds. The bigger yorkies have a different face structure. Their snout / muzzle is longer then the standard 7 pounds and under. Hair color will keep changing until he's appox. 1 1/2 years old but may continue changing. My boy is 6 yo the hair on his back is always changing from black to dark grey, then light grey, now he's like salt and pepper.
Your baby looks like a yorkie to me,
You can always do a DNA I hear the Wisdom Panel is pretty accurate, cost is about $85. It would give you Pease of mind. Check out their website
www.WisdomPanel.com