Its because the colour pattern is a form of agouti, which loses pigment after a short time. In dogs with a melanistic mask the dark hairs are mostly concentrated around the muzzle, although there may be dark shading on the shoulders too. The concentration of darker hairs makes the pigment changes more obvious. So you can get a dog that's solid black and won't grey until it reaches old age, and a dog with agouti colouring that greys when it's little more than a pup.

Thanks xxxxx

nope - she`s blonde! If she goes grey she can get it touched up when she has her highlights done.

shes looks refreshed and young having no grey

aw, he is a handsome chap with his grey hairs.