Blues when younger have a Persian cat colour. As this puppy coat dies it tends to turn a grey colour, at this time the adult coat will be coming through darker than before but a split coat. The longer guard hairs will tend to start to be visible through the puppy coat at around 9 months to 18 months pending the maturity of the puppy in question. An adult coat may have some silver shadings as a black on the tail and the rear of the dog. If a blue is left in the sun for prolonged periods they may start to go a rusty colour. Blues can have a slate colour to their nose and their pigment may not be as dark as a black but should always aim to be.