What is the chance of a border terrier being blue and tan?

The chance of a Border Terrier being blue and tan is approximately 1 in 4 or 25%. This is because the blue and tan coat color in Border Terriers is caused by a recessive gene, meaning that both parents must carry the gene for the puppy to have the blue and tan coat. If both parents are blue and tan, then there is a 1 in 4 chance that any given puppy will be blue and tan. If only one parent is blue and tan and the other parent is a different color, then there is a 1 in 2 chance that any given puppy will be blue and tan.