Until this thread, I used to distinguish me from Anonymous Monk by picking Green Theme (even though I prefer blue palettes, so I actually like the default/Blue theme more than the green), but this conversation had me re-evaluate, and pick Perl-blue (though I customize slightly to swap a:link and a:visited, and I add a:hover), which is distinct enough from the default to make it obvious, tones down the background whiteness a bit, and gives me my preferred blue palette, so it's a win-win-win -- I don't know if it wasn't available when I first set my theme years ago, or whether I didn't go through all the themes, or whether my tastes have changed since then.

But in going through the new themes, and trying to figure out whether I needed a particular class to swap the link/visited colors, I discovered that the theme is enforced by embedding a style tag linking to the right stylesheet node (though now that I reread the original post, I see that was already strongly hinted by the node_id's in haukex's example AM theme). So that means it's easy to look at what selectors need to be set to give a "fully-defined theme" by just looking at each stylesheet node, which means you can make any theme which suits your fancy.

Theme	Mode	Desc
Blue	Light	Default: Blue bar
Green	Light	Like Default, but Green bar
Red	Light	Like Default, but Red bar
Perl-blue	Light	Offwhite background, Blue bar
Dark	Dark	Black background, Gray bar
JBlue	Dark	Blue background, Red bar
Night Shift	Dark	Black background, Green Bar (comments in View Source for a page using this theme imply Corion created the theme)
No Theme	None	Does not include a stylesheet link at all; presumably the best choice if you want to completely design your own theme using the Display Settings's On-Site CSS Markup and/or Link to External CSS stylesheet

So for those who want AM to be dark based on browser settings, and want a different dark theme for their logged in self, to be able to tell at a glance that they aren't logged in, I would suggest seeing if one of the alternate darkish themes would work for your logged-in usage. Or just do a noticeable tweak using On-Site/External CSS. Or create your fully-customized Personal-Dark Theme coupled with picking "No Theme", .

Part of me wants to say that it would be a good idea to honor the OS/browser preferences for even anonymous users, and to switch AM to Dark Mode when their OS/browser asks for it (and that's the part of me that actually wins). Part of me thinks that maybe leaving it the "glaringly bright" default theme would at least discourage some anonymous usage and especially anonymous posting -- at least by anonymonks who don't like light themes. (Anyone want to join me in voting for a nearly-impossible-to-post-theme for AM, which makes the posting form foreground=background and hides the submit button? No? Oh, well.)

But putting aside my anti-anonymous bias, the user-friendly thing to do is to honor OS/browser settings, and have Dark Theme auto-selected for anonymous users who have that browser setting.