SOGo is used for accessing your mails via a webbrowser, adding and sharing your contacts or calendars. For a more in-depth documentation on SOGo please visit its [own documentation](http://wiki.sogo.nu/).
You can change SOGo's theme by editing `data/conf/sogo/sogo.conf`. Per default it uses a blue theme, which you can change e.g. to a green (non-default SOGo-green) theme. More colored themes will be supported in the future.
After you edited said file you need to restart the SOGO container with `docker-compose restart sogo-mailcow` or via the mailcow UI.