Information from Wikipedia:
The Russian Blue is a cat breed that comes in colors varying from a light shimmering silver to a darker, slate grey. They develop close bonds with their owners and are sought out as pets due to their personalities, beauty and coat. It is their short, dense coat which has been the hallmark of the Russian breed for more than a century. The dense coat stands out from the body and one can draw patterns in the coat that will stay until one smoothes them out again.
The Russian Blue has bright green eyes, pinkish lavender or mauve paws, two layers of short thick fur, and a blue-grey coat.he coat is known as a "double coat", with the undercoat being soft, downy, and equal in length to the guard hairs, which are an even blue with silver tips. The tail, however, may have a few very dull, almost unnoticeable stripes. The coat is described as thick, plush and soft to the touch. The feeling is like the softest velvet. The silver tips give the coat a shimmering appearance. Its eyes are almost always a dark and vivid green. Any white patches of fur or yellow eyes in adulthood are seen as flaws in show cats.
The Russian Blue is a curious and tranquil animal. They are known for their friendliness and intelligence, and are somewhat reserved. They have been known to play fetch, open doors, and are sensitive to human emotions. They enjoy playing with a variety of toys and develop loyal bonds to their loved ones and other family pets.
Anecdotal evidence suggests that the Russian Blue may be better tolerated by individuals with mild to moderate allergies. There is speculation that the Russian Blue produces less glycoprotein Fel d 1, one source of cat allergies. The thicker coat may also trap more of the allergens closer to the cat's skin. Glycoprotein is one source of cat allergies, but this does not mean they are suitable to be homed with people allergic to cats; they will still cause the allergy to be affected, only to a lesser degree for short periods of time.
From Pet MD regarding any health concern of the Russian Blue breed:
"There are no specific health problems related to the Russian Blue. It is a genetically sound breed, mainly due to it being a naturally occurring breed. Brushing the coat is not essential, but is a nice addition to the weekly routine of other grooming, such as brushing the teeth. This breed has a particular fondness for human company and will sit quite happily while being combed or brushed, since it is spending time with the one it cares for.
One important note to keep in mind with this breed is its love of food. It will eat beyond its need and ask for seconds, making it a sure candidate for weight related conditions if it is allowed to eat as much as it wants. The best prevention is measuring the food and giving it only at assigned times of the day, and making sure that everyone in the house knows that they cannot give the cat too many treats or scraps."