Thanks for the reports!
We enabled the “default dark mode color scheme id” here on Meta, which now means that all themes will use a single dark color scheme if your browser, or your user preferences, request dark mode.
Obviously not ideal that clicking something like ‘grey amber’ does nothing if you’re in dark mode… so we’ll need work out a solution for that. 
(Gonna move this to site feedback since we now know it’s specifically about Meta)