Following is a brief educational explanation (ie. rant) of basic dog color. Specifically brown versus red. There are two basic forms of pigmentation that a dog can make: Eumelanin (black) and phaeomelanin (red). Each pigment can be altered, made more dilute or more intense, but the base pigment type is always the same. So red can become yellow, gold, cream, or tan, while black can become brown, grey, or blue.
Let me focus for a moment on "brown". Brown is controlled by the Tyrosinase Related Protein 1 gene and is inherited in a recessive fashion. That means that two copies of a mutated form of the gene must be present in order for an effect to be seen. That effect is the dilution of black pigment to a brown color. "Brown" only affects eumelanin pigment, and when two copies of the mutation are present, will effect ALL eumelanin pigment on the dog's body. This includes hair pigment and leather pigment (nose, paw pads, eye rims, lips, etc.). To that effect, since ALL black pigment is changed to brown, it is IMPOSSIBLE for a dog to express BOTH black AND brown at the same time. Think about that for a minute ... a dog CANNOT be "black and brown". Impossible, not gonna happen, try again!
Here are some examples of BROWN dogs ...
And now for some dogs that are commonly called "black and brown", but are NOT BROWN! Pay attention now, see if you can notice what separates these NOT BROWN dogs from the brown dogs above.
Did you see it now?
Brown dogs will ALWAYS have a brown nose. If the nose is black, then the dog CANNOT be brown! Go look again, I'm not lying to you.
Now here are some tricky ones ...
This is a Nova Scotia Duck Tolling Retriever. They are all this color, which is recessive red caused by a mutation in the Melanocortin 1 Receptor gene. That mutation means that it is impossible for the dog to produce any black pigment in their hair. Normally, the dog would be able to produce black "leather" pigment, so their nose and paw pads would be black. But in this case, in addition to being recessive red, the dog is also brown. So his body coat is all red, while his leather is brown in color.