You can change the theme property values by editing the nautilus.css
file. This file may be located here:
/usr/share/themes/$YOUR_THEME/gtk-3.0/apps/nautilus.css
Replace $YOUR_THEME
with the name of your theme. The file requires root privileges to be edited. You can edit the file by copying and pasting the following command in a Terminal and then entering your password:
sudo gedit /usr/share/themes/$YOUR_THEME/gtk-3.0/apps/nautilus.css
Once again replace $YOUR_THEME
with the name of your theme.
When you've successfully opened the file you may now look for the following lines of code. If you opened the file using Gedit you can search using CTRL+F.
...
NautilusWindow .sidebar,
NautilusWindow .sidebar .view {
...
This may look a bit different, maybe only one of the two lines are specified or maybe more have been added, so be patient and look carefully for something similar to the lines above.
You may now look below this code for a line with the following code:
...
background-color: $VALUE;
...
$VALUE
can be any color value and is the background color of your right side menu. You can replace the value by any valid hexadecimal color code or rgb code (among other ways). Examples:
background-color: #00ff00; //Green background
background-color: rgb (255, 255, 0); //Blue background
I hope this helps.