Hmm it just seems strange to me because Ive never seen another like him.
Usually the black puppy coat will turn grey/blue... not tan then grey/blue.
But thats not to say that these things cant happen! I find it really fascinating.
Was he the standard colours (black and tan) as a pup?
If he was all tan maybe he is classed as a 'golden yorkie'?
He is gorgeous by the way.