/usr/share/roundcube/plugins/sieverules/skins/ is in roundcube-plugins-extra 0.6-20111030.
This file is owned by root:root, with mode 0o755.
..
/usr/share/roundcube/plugins/sieverules/skins/default/
/usr/share/roundcube/plugins/sieverules/skins/default/help.gif
/usr/share/roundcube/plugins/sieverules/skins/default/icons.gif
/usr/share/roundcube/plugins/sieverules/skins/default/icons.png
/usr/share/roundcube/plugins/sieverules/skins/default/ie6hacks.css
/usr/share/roundcube/plugins/sieverules/skins/default/iehacks.css
/usr/share/roundcube/plugins/sieverules/skins/default/safari.css
/usr/share/roundcube/plugins/sieverules/skins/default/sieverules.css
/usr/share/roundcube/plugins/sieverules/skins/default/templates/
/usr/share/roundcube/plugins/sieverules/skins/default/templates/advancededitor.html
/usr/share/roundcube/plugins/sieverules/skins/default/templates/editsieverule.html
/usr/share/roundcube/plugins/sieverules/skins/default/templates/setupsieverules.html
/usr/share/roundcube/plugins/sieverules/skins/default/templates/sieverules.html