Full Idea
'Blue' is vague by some standards, for it has borderline cases, but that does not make it a family resemblance term, for all the shades of blue resemble each other in some respect.
Gist of Idea
'Blue' is not a family resemblance, because all the blues resemble in some respect
Source
Timothy Williamson (Vagueness [1994], 3.3)
Book Reference
Williamson,Timothy: 'Vagueness' [Routledge 1996], p.88
A Reaction
Presumably the point of family resemblance is that fringe members as still linked to the family, despite having lost the main features. A bit of essentialism seems needed here.