I think this would be neat as a command rather than having it on all the time. So you would have a keystroke that turns it on and off. Perhaps it could even be on by default.
I bet something like that would be very easy to hack into Emacs on top of its new built-in color theme support. It shouldn't be difficult for other editors either.
That's how I use it with vim. It's easy there to bind a key to `:colorscheme focus-dark` and another to `:colorscheme yourdefaulttheme`. I guess it wouldn't be hard to make one that toggles between both, but I was lazy.
I've often thought that something like this is what's missing from the various online Markdown editors that exist. Many of them have some way of quickly previewing what you've written, which is important, but some sort of content-focussed approach like this seems like it would also be a good idea.
Author here. I've never used LaTeX before. It was just suggested to me that it worked fine. If you open an issue about it with some specifics on what's not working, I'll make sure to look into it.
I bet something like that would be very easy to hack into Emacs on top of its new built-in color theme support. It shouldn't be difficult for other editors either.