Your cat is special -- he's yours, right? -- but his grey coat doesn't necessarily mean he's a Russian blue. Domestic shorthairs' vast gene pool sometimes yields similar traits, but exact lookalikes are rare. It doesn't take James Bond to tell if your cat came from Russia with love.
Unless you've got breed papers on hand, it's hard to prove that grey cat nestled on your lap is a true Russian blue or a domestic shorthair.
Nearly all Russian blues share some traits: a short, dense coat; uniform grey fur, which breeders and fanciers call "blue," with silvery tipping; and green eyes. If your feline friend doesn't exactly match this description, he's probably a domestic short-haired cat. Sometimes the only difference is the eyes or the coat.
Domestic shorthairs fish in a much deeper gene pool that purebred cats. While they occasionally catch some some treasures, it's rare for them to net the Russian blue motherlode.
Color-Coordinated Blue Genes
Cat genetics are surprisingly involved and, ultimately, won't help you tell the difference between a Russian blue and a lookalike domestic shorthair. Still, a brief top-down review helps you appreciate the myriad variables that have to align for an exact lookalike.
In general, short hair is dominant, single-color coats are recessive, base black hair is recessive, darker black tint is dominant, the diluted dark black tint (that's the grey/blue color) is recessive and green eyes are tied to coat color.
Two of the rarer Russian blue traits are their green eyes and their soft undercoat, which is white hair.
Beyond the Physical
If your mystery cat matches the physical description to a tee, but you can't prove he's a Russian blue, it's time to consider personality.
Because their gene pool is smaller, Russian blue cats share similar temperaments. They're social with family members but can be quite independent, they're shy around strangers, and they're quiet and quite trainable, although they won't use a dirty litter box.
Sound like your cat? Keep in mind that the jury's still out on the nature vs. nurture debate. Some Russian blues don't act like Russian blues are supposed to act, too.
The Litmus Test
The only way to really tell the difference between a Russian blue and a domestic shorthair lookalike is by checking their kittens.
If paired with a confirmed Russian blue mate, your cat should (re)produce Russian blue offspring. A pairing between a domestic short-haired cat and a Russian blue cat creates mixed breeds -- essentially another domestic shorthair -- all of whom have a litany of possible coat colors.
If your grey cat is spayed or neutered, this clearly isn't an option. You weren't going to treat your cat any differently anyway, were you?