Day, no question. I prefer white backgrounds, it’s easier for me to look between screen and real world that way. My eyes suck at adjusting.
Yep, that's it. I just changed the text color to red over at /s/chmod. In day mode comment text is red. In night mode it is still that off-white that's hard to read.
Further experimentation needed! I'm on it!
I like my blues mode. :P
It's a browser mod running CSS. It just loads it on the client side. It's more a matter of permissions. If you give everyone access to the sitewide CSS they'll just wreck your site every week. There's nothing that stops adding more selectable themes on the server side, but if you let everyone load they're own from the server side it would eventually just lead to higher storage costs over time. I don't think the increase would be very large in price, but I do think it would make for a support nightmare where inexperienced users wreck their css and cant find the buttons to turn the themes off, and can't find it in the source.
Night mode. I was never really happy with the way day looked, plus I am not a fan of looking at white screens at 2am.
I do use day on mobile though because the dark theme can be difficult to read on a dim screen during the day. I'll have a look and see if I can find some screenshots from around the time the layout was redesigned.
I prefer night mode anywhere available myself.