How bizarre that a single window would use set such a bit to wiggle its palette around (the rest of your colors feel spot on), but hey, it's SGI, they could do whatever they wanted :-).

I also really find it humorous that the diagonal lines in buttonfly all seem to be offset - as letter-based groups, even. Like, all the diagonals from the capital S are laying down just above and to the right of it (mirrored, even). I wonder if they do rise-run encoding for diagonals or some other such trickery instead of the code you've got working now? Pretty cool stuff nonetheless.

Something else I pondered (and will learn from you I'm sure) - I wonder if their GL rasterizer is actually their 2d rasterizer as well? Eg. maybe you don't need a GL context on an X server in Irix - it's all a GL context or something? That'd be pretty rad.