I'm not really trying to get a problem solved here, since the issue seems to have resolved itself at the moment. I'm mostly establishing the issue and the circumstances that it occurred under. I didn't take pictures at the time and don't want to press my luck by trying to duplicate the issue, but I'll come back with an update if the problem reoccurs.
I recently updated my 350m to the 1.7.10/M "Rogue" CFW
I then connected the 350m to my PC to re-install applications and bios files, etc., over FTP.
I left the device to charge, accidentally putting it to sleep with a short press on the power button instead of turning it off with a long press.
When I returned to the device later (~an hour or less), the screen was washed out and flickering with a "halo" of light around the edges of the screen.
I didn't experience the streaky bands of pixels that some people have posted of the original RG 350.
I still had my Toshiba sdhc flashed with the stock firmware, so I switched back, which didn't make any difference.
I switched back to the Rogue CFW and powered on the unit periodically to check in on it. It got better over time and, after an hour or two, the issue seemed to have resolved completely. I gave the unit a full charge (powered off), turned it on, and it's been good to go ever since.
My assumption at this point is that operating the unit while charging, even though it was only in sleep mode, caused the battery to heat up, which disrupted the operation of the panel.
I'll take a look at the inside of the unit when I open it up to install the PSX buttons I ordered from sakura. In the meantime, I'm not going to stop using FTP to manage files.