|These images were provided to me by a reader, Susie, and are copyright to her.|
This is Dandy, a Cairn terrier, and yes, both pictures are of the same dog! Unlike most brindle dogs, Cairn terriers will commonly darken with age. This is the case with Dandy, who is likely to become nearly all black with age.
To express the brindle coloration, he has to express the Agouti locus. Very a rarely a Cairn will appear who is expressing the saddled tan pattern, but overall the breed appears to be near-fixed for sable. As such, Dandy must be AyAy sable.
The red seen in Dandy's coat is rather pale, and I suspect that he is cchcch pale red.
Dandy also has a black mask. Though it is a bit difficult to tell in the first image, it is there. The mask was especially prominent when he was a tiny puppy. The mask appears to be extremely common in the breed. However, recessive red also appears to occur, which would produce the solid creams and wheatens that are found in the breed. I am going to say that he is Eme masked carrying recessive red.
Since Dandy is a brindle, he must also be expressing the brindle gene. There are what appear to be unbrindled sables in the breed, which would be expressing the non-brindle recessive gene. However, I am going to say that Dandy is kbrkbr brindle.
In addition, there must be come other genetic factor that causes the progressive darkening that appears to be nearly unique (if not completely unique) to the breed.
So, that's AyAy cchcch Eme kbrkbr or masked progressive brindle (carrying recessive red).