The SNESManuals.com guy was asking on twitter if anyone had a snes9x version he had used a long time ago that allowed him to set a game's background to a different color, something that's incredibly useful for ripping sprites and graphics.
I've never heard of any SNES emulator that allowed you to do that, so I did a google search and found many people asking and requesting emu authors to implement such a thing, yet all the requests went into to deaf ears.
I assured this person that such a thing didn't exist, because I have been looking for something like this for years too.
Turns out, he wasn't crazy. Apparently someone created a single branch release of the snes9x-rr version that allows you to switch between 3 different background colors by pressing Shift+1 (it's customizable too!), but he never contributed the commit to the main branch, so the feature was never implemented.
I'll try to get the snes9x team to implement this in the official releases, but in the meantime, you can use this release to finally end the many issues dark backgrounds have caused graphic rippers.
https://archive.org/details/snes-9-x-1.51-rrEnjoy!