|Blue Point Siamese - Photo by SweetGirl©|
This cat has some lynx pointing too.
Blue Siamese cats are not bright blue cats all over! I guess you knew that.....Blue means grey or grey/blue and it is an accepted color for the pointing of Siamese cats. It is one of the original color points going back to the mid 1900s. The other "original" colors are seal, chocolate and lilac. Seal, a dark brown or black, is the classic pointing for Siamese cats. The color blue in the cat fancy is a dilute black.
Blue is produced by the allele d "in the formula aaB-dd" (Robinson's Genetics). The color is black pigment (eumelanin) at a chemical level diluted by the effect of this gene. The pigment in the hair strands is clumped rather than evenly dispersed leaving colorless areas giving the dilute effect. Selective breeding can alter the degree of dilution.
The grey cat breeds are blue all over. Some cat associations allow a much wider range of color points that include lynx points (tabby pointing) and tortoiseshell pointing. The pointing is broken resulting in a cat that does not look like a Siamese.