I have a 2008 MacPro3,1 which was patched to run High Sierra. As well, I am running an AMD Radeon 270X GPU (not flashed since I haven't found a ROM for it). The setup has worked fine for some time now.
I've noticed ever since I installed High Sierra that some windows tend to be red or blue. It is more common with
Preview.app and I can trigger it almost every time when I zoom images in preview as below:
I suspect it might either be due to my "non-standard" GPU or perhaps just a peculiarity of macOS 10.13 not completely rendering a square region. However, it is pretty annoying since sometimes I can't get rid of it. I've noticed as well that it appears in the "deep windows" on Time Machine too, though it slowly renders itself to normal (I'd show a screenshot of that, but too much information to blur :-) )
Any ideas? Anyone else experience this?