The schema also carries the flat keys from the pre-list design, which it documents itself.

picture-options, color-shading-type, primary-color and secondary-color are never written, and are read exactly once: when picture-uri-list is empty, to seed the representative entry. That covers a fresh install and the upgrade from the pre-list model, where they still hold the user's placement and colors. The first save retires them.

picture-uri is the exception and is not deprecated: besides seeding as above, it remains the "set as wallpaper" entry point that external applications write. The library never watches it — see Who reads and who writes.