Short answer is no, actually the long answer is also no however you could achieve this with some not so complex dev. I built an Accessibility Hub using category and forum board pages and using a little widget at the top you can change the colour scheme.
Have a play... I guess you could easily save this setting in a custom field on the user profile in a custom field then have each page do a lookup for the "scheme" then render in dark mode
Mine is very basic and these are on some very basic pages, it would be more work to style every single class used across the community but if you want to do this, it's the dev route...
On another note if this was OTB i would use it... I hate white backgrounds, which pains me as my companies primary colour is white.... yeah i know... 🙂
Thanks for the quick and detailed response on this that's really helpful. I think there are definitely a few of us out there who would love it if this was OOB, I use this theme on any app/site I can now. I wonder if posting it as an idea here in Atlas would be useful.
I'll be honest, ideas don't tend to make it into the roadmap quickly however posting it as an idea is absolutely the right thing to do and the process we should follow, post the link when you have an i'll also vote for it as i think it's one of them features the community is missing.
Personalisation is one of the future items on the Khoros roadmap so it's possible this could make it into that stream of work.
Alternatively... I'm no sales man nor am i a developer hence me saying this, I use an amazing agency based in the south of the UK who are absolute wizards on the khoros platform. They have done things with our environment that even people at Khoros have not recognised it's their platform (links in my signature to some of the stuff), if you're ever interested in some excellent value, top class expertise id be happy to make an intro or just check them out Ingleby
Here is the link to the Idea I created, would appreciate any votes from anyone who'd also like this option. Thanks https://community.khoros.com/t5/Khoros-Community-Ideas/Communities-Dark-theme-OOB/idi-p/575787