I'm testing roundcubemail 1:1.2.3-0~kolab3 on Debian 8/Jessie.
In Roudcube's settings menue in skins I have Chameleon, Classic, Kolab (without icon), and Larry.
The skins/kolab directory is empty, and roundcubemail package has the empty directory.
$ dpkg -L roundcubemail | grep kolab /usr/share/roundcubemail/skins/kolab
Removing the empty directory removes the broken skin from settings.
Please remove the empty directory from the package.