Thanks to the efforts of @johani and @stublag there’s now a “Dark” theme you can select for the forums in your user preferences.
I know specific people have asked for this, and complained about the “too bright” default color scheme / theme … I searched and searched a ton of different ways and I knew @AndreBoulay responded about this somewhere, I couldn’t find the reference I knew was there… so hopefully the people who posted about this will see it here!