Greying

Greying, which can also be referred to as silver is a gene (or combination of genes? The exact genetics are unknown) causes a dog that is born black or liver to gradually lighten with age. This is how breeds like the kerry blue terrier and bedlington terrier are born black, but as fully grown are silver instead. It is also the cause of silver poodles and yorkshire terriers, and sandy bearded collies and bedlingtons. If such a dog is shaved down, the new fur can grow out as black before silvering.
The fact that these dogs are born dark and change colour over time separates them from "true" diluted dogs (blues and isabellas) which are born their lighter colour, and do not have black or liver pigment but blue and isabella respectively.

Two bedlington terriers, showing what the greying/silvering looks on a black and a liver dog respectively.

Lowchens often show progressive greying.

Kerry blue terriers often have so-called black points remaining on the legs and tail even when the rest of the body has gone grey. The black on the face is caused by the masking gene.