I am using a computer that started out on 11.10. I have since updated it several times, and installed and used a great number of WMs (Unity, XFCE, Gnome, KDE, Cinnamon). I am not sure how, but somewhere along the way (probably when I upgraded to Ubuntu 13.04), some parts of my desktop theme were broken. I have tried switching themes and installing new themes, but that does not work. Neither did a removal of (and log out/login cycle) the ~/.config/dconf folder work. Specifically: on several menus, the central part of a button icon is a "grey square" that doesn't fit in with the theme (picture below). the window and desktop right click menus looks ugly. The same kind of grey field covers the items, and the square checkbox looks weird (just filled with a uniform blue). The separator is a thick line that looks out of place. It seems to be a similar problem to that of window buttons (picture below).