The working name for the sixth race is the Shadowmen.
And, as you note, one of things that I like to play with is the
layering of ambiguity. Let's say, just for the sake of argument, that
we set up two sides: Shadowmen vs. Vorlons, which looks like evil vs.
good. Fundamentally, I would find that boring. What you would then have
to do is get into WHY they're doing what they do, and HOW they're doing
what they do.
There is, for instance, the "good" that says, "We know what's best
for you, we'll protect you, nurture you, but you'll do it our way, and
we'll keep you away from ideas and beliefs you shouldn't be exposed to."
Okay, maybe that fits one definition of good...but is it?
On the flip side, for instance, there's the "bad" that says "There
must be conflict and death, because it's only through conflict and death
that we grow stronger, that we can eventually create an ordered
universe. The gene pool must be kept strong. To do that, there must be
war and strife and death." Okay, maybe that fits the definition of evil,
but is it?
The key, again and always, is that nothing is what it seems on
Babylon 5. And even if it looks like it IS what it is, you have to look
at WHY it is what it is...and maybe at that point it isn't.
One of the things about this show is that you see as much as you're
willing to see. You can gloss over it, say, "Okay, these are the good
guys, these are the bad guys." But the closer you look, the more you see
the shades. I imagine when the Shadowmen are more fully revealed, some
folks'll think we're going for a basic good/evil conflict...but believe
me, there's a hell of a lot more involved in it than that.