Decency of blonde's cape (8)
I believe the answer is:
fairness
'decency' is the definition.
(thesaurus)
'blonde's cape' is the wordplay.
'blonde' becomes 'fair' ('fair' can be similar in meaning to 'blonde').
'cape' becomes 'ness' ('ness' can be a synonym of 'cape').
'fair'+'ness'='FAIRNESS'
'of' is the link.
(Other definitions for fairness that I've seen before include "Equity, justice" , "Impartiality, justice" , "the fine, dry state of the weather" , "Equality" , "Beauty - justice" .)