Pure blue appropriate (9)
I believe the answer is:
downright
'pure' is the definition.
(thesaurus)
'blue appropriate' is the wordplay.
'blue' becomes 'down' (I've seen this before).
'appropriate' becomes 'right' ('right' can be similar in meaning to 'appropriate').
'down'+'right'='DOWNRIGHT'
(Other definitions for downright that I've seen before include "Plain-spoken" , "True" , "blunt" , "Out-and-out" , "rank" .)