Perhaps the most significant two facts about this cat breed is that it is France’s only purebred cat and the breed standard has remained untouched throughout the breed’s existence in the cat fancy which started in the late 1800s. This is because the intention is to maintain the original appearance. You can see this cat being a companion in the 16th and 17th centuries just as we see it here although it was no a pedigree cat in those days.
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The blue-cream cat coat is a dilute version of the black-red cat coat which describes the tortoiseshell coat so the blue-cream coat is a dilute tortoiseshell. Blue is a dilute black. It is blue-grey. Grey cats are called ‘blue cats’ by the cat fancy as you probably know in recognition of the slight blue hue of the grey. It is between pale grey and slate grey. The purebred cat the British Blue is a British Shorthair with a grey coat.
According to the cat geneticist, Roy Robinson (Robinson’s Genetics) European and American ideals for this coat pattern and colour differ somewhat.
In Britain the colours of the blue-cream should be softly intermingled whereas in the USA preference is given to those cats with segregated patches of blue and cream.
Variants include the following:
Blue-cream and white
Blue-cream lynx point
Parti-colour blue-cream and
Van blue-cream and white.
Gray colour, termed blue by the cat fancy is produced at the dilution or maltese gene locus by the allele d in the formular aaB-dd. The color is chemically black pigment (eumelanin) but with a dilution of the apparent color caused by the clumping of melanin granules in the hair shaft. This results in colorless areas of the hair shaft allowing more light to pass through the hair and thus lightening the color.
Robinson’s Genetics at page 157
On the blue-cream dilute tortoiseshell coat:
The cream and blue-cream are dilute variations from the incorporation of d into the genotype: cream ddO, cream female ddOO and blue cream aaddOo. A pale rather rich cream is preferable for exhibition and these are the animals favored for breeding purposes.
Robinson’s Genetics at page 159
Calico is tortoiseshell-and-white. There probably should be a substantial amount of white otherwise it is permissible to describe the cat as a tortoiseshell.