Blemish allowed to become red (7)
I believe the answer is:
scarlet
'red' is the definition.
(I know that red can be written as scarlet)
'blemish allowed to' is the wordplay.
'blemish' becomes 'scar' (scarring is a kind of blemishing).
'allowed to' becomes 'let' (to let something happen is to allow it).
'scar'+'let'='SCARLET'
'become' is the link.
(Other definitions for scarlet that I've seen before include "bloody?" , "Bright red of clarets" , "Clarets (anag.)" , "Crimson" , "Colour of embarrassment?" .)