Smart, which is auspicious (6)
I believe the answer is:
bright
I believe this clue is a double definition.
'smart' is the first definition.
('bright' can be a synonym of 'smart')
'is auspicious' is the second definition.
(thesaurus)
'which' is the link.
(Other definitions for bright that I've seen before include "Shining; intelligent" , "full of promise" , "Vivid - promising - smart" , "Mentally quick or radiating light" , "Cheerful or quick-witted" .)