One doing work for Violet (6)
I believe the answer is:
indigo
'violet' is the definition.
(indigo is a kind of violet)
'one doing work' is the wordplay.
'one' becomes 'i' (Roman numeral).
'work' indicates anagramming the letters.
'doing' is an anagram of 'ndigo'.
'i'+'ndigo'='INDIGO'
'for' is the link.
(Other definitions for indigo that I've seen before include "Violet-blue dye" , "Blue/violet dye" , "Ellington's Mood" , "Dark blue dye (plant)" , "Blue-purple colour in spectrum" .)