I've been working hard lately on getting the subtle shifts in the backgrounds more accurate. I use a spotlight, so it's usually very bright in one area and gets darker away from that. It's easy to just see it all as one "color" and not pay attention to the values. But I think it's more dramatic this way.
If you haven't already, I'd like to turn your attention for a moment to my buddy, Qiang Huang, who has been doing some really spectacular work lately. Not that he doesn't always, but he's made a leap lately and I'm blown away.