I am fascinated by canine genetics in general but especially canine color genetics. I could go on about other genetics but for right now lets just stick with color and coat genetics. The Hamiltonstovare color has never been truly studied. There are a few assumptions that can be made just by the way that the color is expressed.
The main assumption is that the majority of the population does not carry the liver gene (b) and are probably homozygous dominate for black (BB). Another assumption is that they do not carry the blue dilution (d) and are probably dominate in that gene as well (DD). We can also assume that they have some sort of Irish spotting gene and tan marking gene.
The difficulty with breeding Hamiltonstovare comes with the Irish spotting gene and tan marking gene. Hamiltonstovare does not appear to have the piebald gene (sp) or the solid gene (S). The Irish spotting gene (si) causes the color to be much more static and you can almost predict that the color will appear in certain areas. The one area where there is flexibility is the neck. Currently, it is unknown what causes a white collar or no white collar. For example, in my most recent litter 2 puppies were born with very little white on the neck, one had a large white spot and another had a white collar that faded to a partial white collar. The parents have very little while on the back of the neck.
Another part of flexibility is the tan markings, there are 2 parts of flexibility there. The first part is how much tan is seen and the other part is the color itself. It is currently unknown why the tan creeps into the black because genetically all saddle tricolor dogs have similar color genetics to Bernese Mountain Dogs, Greater Swiss Mountain Dogs, and other Swiss mountain breeds, which is (atat sisi). The theory is that there may be an unknown modifier on a different gene that influences the expression of the amount of tan. Some Hamiltons have large saddle with a minimal amount of tan and others have a slightly smaller saddle with more tan. The color of the tan varies and is related based on Intensity gene (I). The theory is that the variations on the I gene will cause a darker to lighter tan.
The Black gene (BB) within the Hamiltonstovare and other breeds does control the pigmentation of the nose and eye rim pigment. So the Hamiltonstovare will always have a black nose and eye rim pigment. The exception is where white is, there may be some pink pigment mixed in with the black. For example, Hamiltonstovare should have spotted paw pads, this is indicative of the Irish spotting gene.
There is a different black gene (K) that is assumed to be that Hamiltons have the kk gene due to the tan markings and lack of brindle gene (kbr) in the breed. There is an assumption that the recessive red gene (e) is very rare in the breed. The Hamiltonstovare does not have the ticking gene. Some Hamiltons may have the occasional spot on the legs or belly but that is more like a random freckle in humans than a true ticking pattern.
This lack of flexibility within the genes of the breed mean that the only color that Hamiltonstovare will be is tricolor that will change from a Greater Swiss Mountain Dog tricolor to a more traditional hound tricolor as they age. The change should be complete by the time the dog is 2 years old.
Hamiltonstovare should have a double coat that is very dense and short. Hamiltons coat texture will change as they age but the double coat will stay regardless of age. There have been rumors that single coated Hamiltons are in certain lines but I have not seen any proof of that. I also have not seen any studies that show what gene is responsible for a single coat like a Great Dane and a double like Hamiltonstovare.
I hope that there is a study one day to determine the true genetic make-up of the Hamiltonstovare coat. I think that they would be an ideal breed to finally figure out where the modifier of the tricolor saddle lives, as they only produce that color.