Determining if your cat is a Russian Blue mix can be tricky without genetic testing, as many cat breeds and mixes can have a similar appearance. Physical characteristics such as a dense blue coat, a muscular build, and green or blue-green eyes are typical of a Russian Blue, but these can also be found in other breeds or mixes. The best way to know for sure is to consult with a vet or a professional cat breeder who can help determine your cat's lineage.