What do I need to look for so my yorkie puppy's hair won't go gray?

I am getting a yorkie and all the pictures that I have seen of full grown yorkies they have gray hair, but my friend, who has had his yorkie for 6 years, is still that same black and brown color that the puppies are. So how do I know which puppy wont go gray.

The color is called "blue". They are supposed to turn blue. It's in the breed standard.