This is not a proper solution, just a work around so that setting dialogues work (I have the same issue). This only seems to happen with the default elementary GTK+ theme. If you switch to another theme (HighContrast is also installed by default) then the issue is gone for me. Alternatively using the default theme, but then switching to dark also works for me (that's what I use now). Forcing a re-install of elementary-theme (sudo apt-get install --reinstall elementary-theme) does not solve the issue.
The best way to change the GTK+ theme is using gsettings. To switch to a different GTK+ theme open a terminal and run:
gsettings set org.gnome.desktop.interface gtk-theme "HighContrast"
Replace "HighContrast" with the name of theme you want to use. The default theme is called "elementary" if you want to switch back.
To switch to dark edit ~/.config/gtk-3.0/settings.ini in a text editor. For instance open a terminal and run:
This opens the file in nano. Replace gtk-application-prefer-dark-theme=0 with gtk-application-prefer-dark-theme=1 . Save, close the file (Ctrl + O, Enter, Ctrl + X) and log off and on for the change to take effect. If the file does not exist then create it with the following content (for dark theme):