Silver color in dogs is because of a recessive gene, and in Cairn terrier it is no exception. The silver and silver brindle variations are the standardized color of this breed as per the American Kennel Club and other notable registries like the United Kennel Club, and the Federation Cynologique Internationale (FCI).
Silver Brindle
Silver brindle is a result of the G locus or graying gene. They initially have a black coat that turns gray upon dilution as the dog ages.