Change background color of selected text

You can edit

/usr/share/themes/Ambiance/gtk-2.0/gtkrc
/usr/share/themes/Ambiance/gtk-3.0/gtk.css
/usr/share/themes/Ambiance/gtk-3.0/settings.ini

and wherever you see selected_bg_color change #f07746 (orange) to #0000ff (bright blue, or whatever color you prefer)

These are system files, so to edit them you'll need to be root like so:

 gksudo gedit /usr/share/themes/Ambiance/gtk-2.0/gtkrc /usr/share/themes/Ambiance/gtk-3.0/gtk.css /usr/share/themes/Ambiance/gtk-3.0/settings.ini

Related