I don't suppose they have any updates to their ATI emulation?
Well there are no "Updates" to single components anyway. But this is the current version of parallels 8. Guessing that it has to do with the ATI background is wild anyway. Actually I never had anything similar and I tried a lot of games in Parallels 8 without noticeable differences between iMac and MBP.
I just tried to switch the iMac Virtualisation from "Experimental DX 10" to "DX 9" but that did not change anything. I also used different Screen resolutions. Steam and none Steam versions. Reinstalled everything and so on.
I am trying to install it on a "non Bootcamp" virtual machine with WinXP next
I also tried it with Wine but had multiple problems immediately with FE getting not even close to work at all.
Well.. in December I get one of the new iMac which will be NVidia based... haha!