Corrupted Login?

Out of nowhere my late 2013 27" iMac running OS 10.14.5 puts up a yellow/green screen through which I can barely see any icons. This is not a "tint" but a full color error. No response to any mouse clicks. It was fine in the morning and faulty in the afternoon when I returned to the computer. If I boot up in Safe Mode, the computer behaves normally and the screen looks fine (aside from missing extensions, etc.). I tried rebooting many times, resetting PRAM/NVRAM, reset the SMC, all to no avail. If I create a new user or login as Guest, everything behaves predictably, though limited.

Clearly this is a software problem, but I have no idea how to proceed. How do I determine what is causing the problem so I can remedy. Reinstalling the OS or even just working from a new Login means I lose all of my menu bar items and I presume would have to reinstall those apps. If I use a new Administrator login, how do I get access to all the documents etc. that are associated with my corrupted(?) system?

Thanks to anyone who can point me in a direction to explore. In the old days one could turn off extensions one at a time - I don't think there's a way to do that now, right?