Blue

Different countries are using different symbols for the genes that give the two "blue" colours giving rise to quite a bit of confusion. The gene that gives British blue (which also gives English blue, American blue, sky blue, slate blue, powder blue, whatever your chosen terminology is) has been scientifically described as "d".

• D - Wild type dominant, a "no effect" gene
• d - Dilute (recessive). Dilutes black pigment to give a range of blue shades including sky, slate, British (aka English), American, and powder, has a slight dilution effect on yellow pigment.

No other mutations at this locus have been confirmed - it has been theorised that some of the shades are caused by separate alleles although this has not been proven.

 

a/a D/-	Black
a/a d/d	British blue
A/- d/d	Blue agouti
a/a d/d	American blue

Russian Blue

It is fashionable in the US to give Russian blue the symbol "d". Russian blue has not been scientifically described, though in the fancy it is commonly referred to using the "rb" designation:

• Rb - Wild type dominant, a "no effect" gene
• rb - Russian blue (recessive). Dilutes black pigment to a distinctive heathered metallic blue, has a slight dilution effect on yellow pigment.

No other mutations at this locus have been confirmed.

 

Rb/-	Black
rb/rb	Russian blue
A/- rb/rb	Russian blue agouti
d/d rb/rb	Russian Silver
A/- d/d rb/rb	Russian silver agouti

German, Midnight, Leaden

Occasionally breeders across the world claim third blue varieties. In Europe there have been claims of a third shade called German Blue, in America a new gene has been called Midnight Blue, and "Leaden" has been talked about in the past. While these varieties may well exist genetically they have not been widely bred or standardised in the fancy.