Took him to the groomers today, got him back and he changed colors!

He's DARKER again. He was all black and tan as a pup like all Yorkster's, then turned to a whiteish, which then turned more silver... now that he got shaved again for his summer cut, he's dark again! Not quite black, but wow! I love it.
It's probably harder to tell in photos but in real life-- there's a striking difference!
He's 1 1/2 years old. I wonder if this is going to be his more permanent color?
First pic was taken yesterday and the others were today!