The Jack Russell terrier is a small dog that can come in different colors including red, black and tan. The Parson Russell terrier is also a small dog but has a long coat that is colored black andtan or light brown. FoxTerriers are the largest of the breeds and are usually either red or sable. They have a short tail and oval shaped heads. The Russell Terrier is the most popular Jack Russel terrier and comes in both wirehaired and smooth coat varieties.