Noble Neutral takes place in a world where everyone is generally good, but the world could use some fixing. It is a common setting for light heroic fantasy, because there are many heroes, and the bad guys are simple, but the world itself still offers some challenge. It is a pretty nice place to live, right up there with neutralbright.
Neutralboring is boring because we are here right now. Reality, unless you have some skewed or stupid view of it, is the standard. This alignment exists mostly to tell you how to choose a more appropriate one, because if we wanted to adventure in neutralboring we coudl just go outside. Common for people who are too lazy to build better worlds.
Neutraldark is a pretty bad place to live. The world sucks, and the people don't seem to care all too much. This is not so much a dramatic setting as it is a nihilistic setting; the world sucks and nobody seems to care. It is the place for insignificant heroes who futilely rail against the publically-popular villains, and defeat them, only for another to rise just as soon after. It is a depressing setting, all up, and common for mundane (that is, not heroic) fantasy.