Board Thread:Support Requests - Getting Technical/@comment-31402001-20140416190838/@comment-168424-20140416221106

There is no easy way. If you can find one of the available themes in Special:ThemeDesigner that matches the text color you want that is the quickest way.

The alternative is lots of CSS in MediaWiki:Wikia.css.

A similar discussion occurs at length here about this topic: How to get black text on white background?.