"Or the fact that Poser/SuperFly applies gamma correction to a color that I plug into a value input, so I have to reverse that in a math node...

... Nah, that gamma correction issue is a bit more specific, and  the texture node settings didn't seem to make any difference. I'll probably ask about it in the technical forum later, rather than have it buried in this thread."

Says this in Dimension3D's 'Introduction to Superfly' pdf...

 
https://www.renderosity.com/mod/bcs/introduction-to-superfly/112622

and that's it. Apparently, according to this it's omnipresent. All of my forum searches return the same prognosis... GC is always present and no mention of a workaround.