Although it is currently a dark mode, only the menu interface is dark mode, and the document viewer that occupies a large area does not support dark mode.
We ask that you support document mode in the document so that users can use DT3 more closely by reducing the burden on visual impairment.
Are you able to view the same document in dark mode in other apps, such as preview?
It is my limited understanding that only a few apps support dark mode for pdf files but that doesn’t include Preview - which is the same API that DT3 is based upon?
I doubt that that’s possible. PDF is a document format which is meant to be printed (or at least it was). PDF is all about presentation. Dark mode doesn’t make sense in this context.
Whereas HTML documents (for example) are primarily structured documents that can possibly be presented in a myriad ways. That’s what style sheets are for, and you can easily define a dark, twilight or light mode for any HTML document if you’re so inclined.
Not so for PDF – there are not “styles”, all the presentation information is part of the document itself. Which is also a good thing. You would not want you PDF to be stylable like HTML, because than it might be possible to display parts of it “white on white” (or “black on black” in dark mode).
Not something one would want with possibly legally binding documents.
Isn’t it technically possible to convert a document to dark mode or sepia mode, as shown in other popular PDF programs I’ve illustrated?
It might be technically possible. Personally, I wouldn’t want any PDF viewer to change the document in any way without my say-so. PDF is meant for print. If I can’t trust the viewer to show the PDF as it has been programmed (yes, PDF is based on a programming language), I can’t trust it at all.
TL;DR
DT3, like Apple’s Preview app, presumably use Mac OS’s built-in PDF library/interpreter. If that piece of software doesn’t support dark mode, the DT3 and Preview don’t, either. PDFExpert, MarginNote might provide their own PDF library/interpreteror they might just manipulate a color lookup table.
Acrobat Reader doesn’t use dark mode (and that is or was the gold standard for PDF display), neither does PDFPen (two more “popular PDF programs”). So there doesn’t seem to be a clear majority in this case.
PDFExpert can do it, it doesn’t change the PDF, it just changes the view (on demand)
I would definitely vote for this feature. Even if DEVONthink just put a rendering filter to “flip” the colour, I would be happy with that.
As already mentioned, MarginNote 3 has an option to do it, and it works under the Apple PDF Render Engine. I would think it is possible.
In DEVONthink 4, did dark mode in PDF files ever happen? I realize anything like that must be a lot of work. I want to stay in DEVONthink and not move over to PDF Expert.
In Tahoe, it seems, macOS Preview has a dark mode toggle in the View panel. At least according to this StackExchange thread.
I agree PDF documents are not intended for reader styling.
However it is certainly reasonable to offer inverted viewing (or even inverted printing) for accessibility reasons where black turns white and white turns black.
I’ve yet to find a dark-mode web site that I don’t turn away from in horror 
Personal taste or aging eyes. The worst are those that force dark mode on me without offering a choice.
While there may be reasons for white on black on screen, I don’t see any for that in print. Not to mention that simply inverting colors does not necessarily help legibility. The fonts would have to be adjusted, too. That’s at least what knowledgeable people do in traditional printing. Otherwise, the dark color visually or physically damages the fiber lines of the font.
It’s interesting: I’ve used to be a big fan of dark mode everywhere (not all the time, but once it’s dark outside).
but now I disable it whenever I see it — I simply cannot read or use the screen comfortable if it’s in dark mode. Dark on white is the default mode for me. And I’m in my 30s.
Macular degeneration, cataracts, and migraine headaches are 3 classic visual conditions where people often prefer dark mode.
In theory this would be helpful in print as well if printers with white ink were readily available - but they are not very common, and the absence of black ink is not as useful as actual white ink.
Since inverting colors on a screen is much easier than printing with white ink (and costs basically nothing) dark mode is much more common on computers than on paper.
