Sounds like another "improvement".
AutoCAD replaced its VERY serviceable renderer with "Mental Ray". FABULOUS ray trace renderer, but they didn't duplicate the previous setup by setting the Mental Ray settings to match by default so results could be usable "out of the box" with just final tweaks for improvements, so its a bit of a challenge to adopt. The results CAN be STUNNING(!), but if they'd have augmented instead of replaced it would have been better for the user, but then fewer users would have put in the effort to master the "improvement", with the basic renderer being so useful.
If you DO get an answer to the background color thing, please post back here ! We'll be monitoring for results...
Good luck !
- C.