User blog comment:MisterWoodhouse/The first Unified Community Platform release is now live for NEW wikis/@comment-1998339-20200313113046/@comment-1998339-20200313150933

Nonexistent categories appear red on that wiki because of lines 559-562 of your wiki's Wikia.css page. Technically, per Staff's responses here, that constitutes a violation of the Customization policy. Wikia changed vanilla category link behavior back in 2011, forcing nonexistent & extant categories alike to display as bluelinks.