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This dog is clearly a great Dane and is expressing a rather common breed color that comes from harlequin-harlequin matings: "white." White Danes are always of a very predictable genotype.
To begin, this dog must be dominant black. All Danes that are black, mantle, harlequin, and blue are expressing this gene, while the brindles and fawns are expressing other variants of the K-black locus. Though its possible she is carrying one of these other variant, due to color class breeding within great Danes this is highly unlikely. Thus, this dog must be KK black. Though the color that is seen on the dog appears to be a bit grey, this seems to be due to aging rather than anything else.
Next, this dog is merle with the harlequin modifier. All harlequin Danes are heterozygous for the harlequin modifier, which causes the lighter patches due to the merle gene to be diluted to white. The gene is lethal in the homozygous form, which is why harlequin never breeds true and non-harlequin merles will appear in litters. All harlequin Danes are also merle, with the dogs that are acceptable under the breed standard and are seen in shows being mostly all single merles. Since harlequin-harlequin (and thus merle-merle) matings are commonplace in the breed, double merles will definitely occur. If these double merles also have the harlequin modifier, they will end up looking like this dog: white. So, this dog must be Hh MM double merle harlequin.
Harlequin dogs are very often bred to mantles, and dogs with clear white collars are, at least to some extent, preferred in the ring. As such, Irish white is very common in harlequin great Danes. Due to this, I suspect this dog is also sisi Irish white.
So, that's Hh KK MM sisi or white with black patches.