Hi there,
don't know if this is intended, a dokuwiki or GeSHi bug. It appears to me that Dokuwiki is using hardcoded css styles instead of the per language definitions found under inc/geshi/ for each language geshi supports.
The keyword 'public' should be colored #0600FF for <code csharp> ( line 176 inc/geshi/csharp.php ) actual used color is #b1b100.
http://dokuwiki.philipp-stader.de/ has an example right on the start page with screenshots from the geshi examples page for easier comparison.
Thanks!