I think Esperknight and I agree that white is out. It's so bland and out of place that it ultimately more of a compromise than any compression-gunk that forms around yellow subtitles.
For yellow, we can raise the brightness level of it slightly to reduce the gunk around the letters. I don't want to do it too much, though, or it winds up looking a bit washed out.
Have you tried other color options? The yellow honestly looked a bit "90's fansub"-esque, if you get what I mean. (Particularly, they look like my old VHS Fansub Nippon Gold Dragon Ball Z tapes.)
Now, on the other hand, perhaps that was the idea...?
I would suppose a dark "military-esque" green or beige would also fit the atmosphere... Either that, or go with colors that match those for in-game text.
I never thought of 90's anime fan-subs, but considering how old-school this animation is, there's nothing wrong it looking like that.
The problem with other colors is that they're always going to be on a black background, so we're limited to light shades. I have to politely disagree about military-esque colors fitting the atmosphere, though. Most of the cutscenes take place in space, and there are lots of inorganic colors from across the spectrum. Military shades are a little earthy, more natural and fit a limited color range.
If anyone is interested, here's a couple of screenshots with yellow subs and some pixel junk. It looks fine on an LCD screen, and you don't see how it changes around in these static images, however when playing on a CRT set, this stands out a bunch more. It's still not that bad, though, and you'll have to enlarge the picture just to see it.
http://dl.dropbox.com/u/32377930/zero-0007.pnghttp://dl.dropbox.com/u/32377930/zero-0012.png
