MySkin is, as I understand it, an attempt at a blank slate. However, it does include MediaWiki:common.css (and skins/common/commonPrint.css and skins/common/shared.css)
There is a suggestion that "redlinks" (a.new), viewed on MySkin, used to render in red. That would suggest to me that users using that particular skin used to be given skins/common/commonElements.css, which defines the redness of redlinks.
I can't believe that changing the display of a skin being used by people was intentional-more likely an unintentional side effect of tidying up CSS dependencies.
Could someone confirm?