After I switched some wallpapers manager apps I got the problem: XFCE4 Wallpaper only display in black and white. I have managed to fix the issue partially, by removing and reinstalling
gdk-pixbuf2 – which I recall threw some errors during the system update. However, all custom (jpeg or png) wallpaper images are displayed in black and white once they are set as wallpaper.
cower: error while loading shared libraries: libalpm.so.8: cannot open shared object file: No such file or directory