The unique feature of the Russian blue rat is the heathering in the fur, which almost looks like ticking in some cases (this is caused by “clumps” of pigment in the fur). This is unique among colours in the rat, but it’s actually common in blues of other species as they are more similar to Russian rat than British blue rats.
The heathering in Russian blues is supposed to be subtle and faint, too much of it is suppsoed to be a fault but many Russians have loads of heathering. As a variety they are prone to silvering and quite plain heads, but their colour tends to be rich to the roots and, as long as you don’t let it get brown, very attractive rats. They’re a robust and healthy variety too, and as such tend to be quite popular with both breeders and pet owners.
Genetics: non-agouti with the Russian blue gene (aarbrb)
NFRS standard: Colour to be similar to blue cats and dogs. A soft medium grey-blue with a metallic sheen. Faint light speckling or a subtle ticked effect (heathering) is usual for this variety and is not a fault. Colour to be even, belly colour to match top. Undercolour dark blue down to the skin. Eyes black.