User blog comment:Vegeta88/Colored Comment?/@comment-4674838-20120918204209

You can... but without putting it in MediaWiki:Wikia.css, only you will see your comments as being colored. They will not look colored to other people, just yourself.

It is impossible to have any CSS affect other people without putting it in MediaWiki:Wikia.css or some other MediaWiki: page (which requires you being an admin in order to edit it)

See Help:JavaScript and CSS Cheatsheet for more information.