You can add a new option for the icons setting in the Theme preference tool. Icons options reside in the /usr/share/icons/option-name directory. The typical structure of an icons option in the file system is as follows:
/usr/share/icons/option-name
/usr/share/icons/option-name/icons/*.*
Typically, a new option for the icons setting is supplied as a .tar.gz file. To install the new icons option, unzip the .tar.gz file, then untar the .tar file into the /usr/share/icons directory.
Users can install their own options for the icons setting. If a user installs an option for the icons setting, the option is stored in the $HOME/.icons/option-name directory.