User blog comment:Kirkburn/Technical Update: August 31, 2016/@comment-26402117-20160901131645/@comment-26402117-20160901180355

I'm thinking blue also matches up with the hue of the dark Wikia logo and the site's default URL color. The orange shade is simply the inverted hue.

As a note, added content may be constructive content or not - with the same applying to removed content. I'd argue that using more neutral colors would prevent attaching connotations to diffs as well as improving accessibility.

Aesthetically, red and green are also harder to use in color schemes.