None of my "melanurus" have the nearly pure black tail associated with the classic Blacktail Cribo. As a matter of fact, most of them that I see don't, but the tails are noticeably darker than the rest of the body. I suspect that most of the wild-caught Blacktails that come in are actually intergrades...maybe mostly Blacktail, but somewhere in the lineage intergraded with unicolor. The pure Blacktails that I've seen have a black tail, or nearly black. Mine have a tail that is 2 or 3 shades darker than the rest of the body, but not even close to black.
There is a thread above this one in which Dean discusses intergradation of melanurus in the wild.