A suggestion: card- or grid-gallery views should be able to have a different background color from the feed/thread view: namely dark background instead of a light one

[decadent]

For me, feeds and threads are better viewed in the light theme. Meanwhile, images are better viewed on a dark background because a) it focuses the view on the image itself, and b) images are basically guaranteed to be darker overall than a light background, by the nature of containing darker areas (which is a perennial problem on the web). RedReader already shows individual images on a dark background, regardless of the theme — but, a dark theme on the gallery views is useful too.

The app already has dark themes for the gallery, synced with the overall theme. My suggestion is to add a toggle to use the dark gallery theme instead of the main theme — perhaps in the gallery's options under the gear icon. Or, to just do it always like with the image viewer.

I think all the light themes map to ‘Night’ as the dark alternative for the gallery. (Though I myself am partial to the minimalism of ‘Ultra black’.)

A potential problem I can see is that captions for the images would be displayed in a light color on a dark background, contrary to the main theme. But imo that's a small price to pay for the more-frequent use-case of looking at just a bunch of images.