You can edit the gtk-main.css
or nautilus.css
files.
I recommend you to try this under your ~/.themes
and not system-wide. You may either change the background color of nautilus only or the base theme as a whole, which affects a lot more programs. In this example I will change the background color in the default Ubuntu Theme "Ambiance" (in Ubuntu Gnome use the folder Default instead) from white (#ffffff) to a light grey (#D8D8D8). Feel free to pick any other color.
For comparison how it looks like in the beginning:

Create a copy in ~/
Create your ~/.themes
directory and copy the original Ambiance theme to it.
mkdir ~/.themes
cp -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.
nano ~/.themes/Ambiance/gtk-3.0/gtk-main.css
Change this line:
@define-color base_color #ffffff;
For this one:
@define-color base_color #D8D8D8;
To save the changes in nano, press Ctrl+O,Enter then Ctrl+X.
Effect:

Change the background color for nautlius only
If you want to change the background color for nautilus, edit nautilus.css
.
nano ~/.themes/Ambiance/gtk-3.0/apps/nautilus.css
Add this lines to the beginning of the file.
NautilusWindow * .view {
background-color: #D8D8D8;
}

To save the changes in nano, press Ctrl+O,Enter then Ctrl+X.
Effect

To see the changes you can restart nautilus, logout login or restart your machine.