Do border terriers get lighter in colour when they turn from pups to adults?

Yes, border terriers can get lighter in colour as they mature from pups to adults. The coat of a border terrier pup is typically a deep blue-grey, and it gradually lightens as the dog ages. This is due to a decrease in the amount of melanin in the hair follicles, which is responsible for giving the coat its colour. By the time a border terrier is fully mature, its coat may be a much lighter shade of blue-grey, or even a silver-grey.