In my experience black back has been used as a general term to describe very dark black back. Similar to a reduced patteren ther is no guarantee of genetics its just more of a descriptive term.
Now if someone says genetic reduced or blackback then that changes the impression to say yes this is a proven trait.
Like any trait there are variations. I have seen pastels (that I know are genetic) that are so dirty in color that an untrained eye might mistake them for a normal. So judgement always come into play when making a purchase.
I would say yeah you can call that a black back. How nice of one is up to personal opinion. Beauty is in the eyes of the beholder.
Black backs dont need to have a pure solid black stripe to be called black backs.. As long as they are black back from head to tail with very few breaks they can be considered black backs. Then you need to prove them out for them to be worth more then a normal. Mine are codom black backs.
I think shes a black back, and if I had the cash I would buy her. I need some close to breeding age females. My girl looks just like the normal colored BB in the pic.