ἅτις κυανεᾶν οὐχ ἅψατο Συνδρομάδων ναῦς, 22
Now in first declension nouns, no matter where the accent is in the nominative, in the genitive plural the accent is perispomenon, νίκη, νικῶν. This is presented as a rule in most textbooks, but if you know Epic then it's clear that the accent is the result of the contraction of -άων (long alpha).
In Attic, first and second declension adjectives have forms and accenting identical to the nouns except for the feminine first declension genitive plural, which is accented like the masculine/neuter form. Thus, in Attic ἀξίων γυναικῶν not *ἀξιῶν γυναικῶν. Homer, however, keeps the full -άων ending (or derivatives of it, -έων, or after vowels -ῶν).
So what's going on with κυανεᾶν? Not one of my grammars has anything to say about this. From the form it's clear that this is a Doric (or Aeolic) contraction from -άων, so I was prepared to accept the accenting in all the editors of Theocritus I could find. I still wanted some clear statement about this, however. Finally I had to resort to an accenting manual, Chandler's A Practical Introduction to Greek Accentuation (GoogleBorg), which is actually a massive work. The very large section 203 (p.55) starts with,
Feminine adjectives and participles following the first declension (which in the oblique cases of the singular and in all cases of the plural are subject to the rules laid down for oblique cases in the first declension) present some peculiarities.
He then goes on to citations from the ancient grammarians. Then, section 204 (p.56),
The Aeolic and Doric genitives in αν are circumflexed, as κυλιχνᾶν, Τηϊᾶν, ...
So there you go. You need never worry about this perplexing matter again.