User blog comment:Kirkburn/Technical Update: April 23, 2013/@comment-1175135-20130430045704/@comment-3335785-20130430075122

Wikia use the standard diff from MediaWiki 1.19 iirc. It was updated in 1.20, as you can see on wikipedia. The diffs Wikia use can be altered with CSS to the newer diff styling, such as seen here.