I've noticed that in some cases when a dog is black, at least to my eyesight, they are described as being blue. Here is, I think, an example of this, in a Doberman:
I know you might say that the colors in the particular photo give the impression that it has a black coat as opposed to blue, but I recently saw the papers of one dog that had "blue and white" written for "color" when I could swear it was black. I stood there a while, closely looking at what was supposed to be its blue-colored hair/fur, looking at it from different angles to see if the light made a difference, and either I must be colorblind or it was black, not blue.
Does anyone know why seemingly black hair/fur on dogs is called blue?