Oh, forgot to add the screenshots: https://computerfairi.es/media/cXy7hxUM8Wk31hZyByQ https://computerfairi.es/media/b44ZNGF0TsCLILSdhM0
Still, as of now, individual users are responsible for making this service accessible to them, because the default is one that is hard or impossible to read for many people, and there is no built-in way to change these things. There is talk about all of this on Github, so I am hopeful. But really, right now, this is… not a good situation.
I'd also like to point out that I didn't pay enough attention to these things until I saw someone's tweets today about how this is not working for them, at all.
And that is one way that exclusion happens, when you don't take issues that you know about theoretically THAT serious, because you are not personally affected.
If you can generally handle light text on dark background, but need some contrast improvements to the original theme, toot.cat has that: https://toot.cat/users/ashkitten/updates/15381
This firefox addon (via @Antanicus) is named after doing the opposite, but you can change the settings to get a light background and dark text: https://addons.mozilla.org/en-US/firefox/addon/dark-background-light-text/ (just be warned, while doing so, the description of which color is which will not be readable if you just switch the two … in retrospect, obviously *confused cat* m)