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This dog is a tosa inu from and is of a color that appear to be somewhat uncommon. Why is that? I must say this is the only tosa I have ever seen that has been blue. So, that's this dog's genotype?
To begin, since this dog is has both red and black pigment, it must be expressing one of the alleles on the Agouti locus. It appears that the vast majority of tosas are sable, which this dog is, but some of the breed are tan pointed. Though this gene is present, it isn't very common and thus this dog is most likely AyAy sable.
The intensity of the red on this dog is rather dark, and as such it's most likely CC dark red.
Next, this dog is blue. There is a distinctly greyish caste to the dog's coat rather than black, and the dog also has pale eyes. The blue dilution gene is recessive, so this dog must be dd blue.
This dog also appears to have a dark mask, seen in the uniformity of color on the muzzle and above the eyes. The gene is known to occur in the breed, though it is far from fixed as many dogs are maskless. Since this is true, I believe this dog is EmE masked carrying non-masked.
Last, but not least, this dog does have white markings on its neck. Though there is the occasional tosa inu with Irish white markings, I suspect that this dog has residual white. This is not an uncommon occurrence in dogs that are genetically solid, and appears to be a natural quirk of canine development. That would make this dog SS solid with residual white.
So, that's AyAy CC dd EmE SS or blue brindle with residual white.