Interesting questions, Jack. In my experience, what I see -- or saw, since it's been a long time -- when looking through a 14 inch or smaller telescope (I've never had the pleasure of riding high on a 200 inch one) was dramatically different from what the professional astronomers turned out. Even with a 14-incher, there are a lot of objects that you look at out of the corner of your eye to make them appear bright enough, and now you're using strictly scotopic vision (which is why you perform that little trick in the first place). Even bright nebulae look pale through a small scope compared to the shots the big boys (or the Hubble) take. I've also noticed that when looking at the Milky Way with bare eyes that it looks a lot paler than all the shots that I see now that digital photography has made taking images of our galaxy falling-off-a-log easy.
So I question the whole idea of the viewer's adaptation when looking through a telescope as the basis for adjusting the colors in astro images. I think they are what they are in terms of color, and any way that you get them to look "right" (and right is now defined for many as "like all the other astro images, and maybe in particular by the ones from the Hubble) is fair game.
Jim