The right sort of blonde is impetuous! (4)
I believe the answer is:
rash
'impetuous' is the definition.
(I've seen this before)
'the right sort of blonde' is the wordplay.
'the right' becomes 'r' (abbreviation).
'sort of blonde' becomes 'ash' (ash blonde is a hair colour).
'r'+'ash'='RASH'
'is' is the link.
(Other definitions for rash that I've seen before include "complaint" , "Hives" , "sign of irritation?" , "Skin redness" , "Hasty; series of things" .)