I've just figured it out. One of my package.ymls I had tried included a line something like this:
install -Ddm00644 themes $installdir/usr/share/themes/
The problem with this line is that it sets the permissions on the themes folder to r--r--r--
instead of r-xr-xr-x
. Since Budgie-Desktop-Settings doesn't have execute permissions, it can't apply the themes. And since the permissions got set on the entire themes folder, none of my other installed themes worked either.
The line should have been:
install -Ddm00755 themes $installdir/usr/share/themes/
which would have set the file mode bits correctly for execution. Since I'm using %make_install
now, this doesn't matter anyways, but it's good to have figured out the issue.
I fixed this by executing sudo chmod -Rf ugo+x /usr/share/themes
in order to correct the file mode bits on the themes directory and its contents.
Thanks to all for your help and suggestions. This issue is now resolved, and I have the themes (including Skeuos) working on my system via my own package.