change backgroud color of the windows in ubuntu

Create a copy in ~/

Create your ~/.themes directory and copy the original Ambiance theme to it.

mkdir ~/.themescp -R /usr/share/themes/Ambiance ~/.themes/

Change the background color for the whole theme

If you want to change the base color for the whole theme, edit the base_color (Hex notation #??????) in gtk-main.css. This changes the background color of other applications (eg: gedit) as well.

gedit ~/.themes/Ambiance/gtk-3.0/gtk-main.css

Change this line:

@define-color base_color #ffffff;

For this one:

@define-color base_color #C7EDCC;

for more details see: http://askubuntu.com/questions/465908/how-to-change-background-of-nautilus-in-ubuntu-14-04