Dye from one doing pants (6)
I believe the answer is:
indigo
'dye' is the definition.
(indigo is a kind of dye)
'one doing pants' is the wordplay.
'one' becomes 'i' (roman numeral).
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'doing' is an anagram of 'ndigo'.
'i'+'ndigo'='INDIGO'
'from' acts as a link.
(Other definitions for indigo that I've seen before include "Blue/violet dye" , "Deep violet-blue colour" , "Mood - (Duke Ellington)" , "One of the colours of the rainbow" , "Spectral colour" .)