I don't know if this is a well-known design rule or not, but it should be, and I've just implemented it: the colors used for permalinks should be consistent with those used for "visited" links, even if they can't be automatically identified as such by the browser. A permalink never points to content that the user hasn't seen already (except in blogs where the permalink is also how you get to the comments... but that's a different issue). The permalinks here were previously way too prominent, and I couldn't reduce their font size without breaking my previous decision to use 100% for everything.