This is a term I’ve always associated with the Firefly theme song, and in fact, had assumed was one that Joss Whedon had made up (and he may have done so, independently). It turns out that the OED SF citations project has a cite for this as well, although it’s only in the quotation for “spacer” (it’s the 1986 cite), rather than as its own catchword. Now I’m wondering if this use is actually more common, or whether these are two isolated instances. There’s no easy way to determine this, of course — I haven’t encountered it elsewhere in my research, and nobody has suggested it to us at the OED project, and there searching for instances of “the black” in places like Google books and Amazon (which both have good collections of recent SF) is a completely futile endeavor. Even a corpus might have difficulty with it, since “black” can be a noun in other senses. I’m not betting on its being very common, so I’m not bothering to put it on the OED site (we have a backlog of many much more promising suggestions as it is), but I’ll have my eyes out for it, nonetheless.