Dark skin blemish - reticent about that (7)
I believe the answer is:
swarthy
'dark skin' is the definition.
(I've seen this before)
'blemish reticent about that' is the wordplay.
'blemish' becomes 'wart' (wart is a kind of blemish).
'reticent' becomes 'shy' (both can mean withdrawn or timid).
'about that' means one lot of letters goes inside another.
'wart' inserted into 'shy' is 'SWARTHY'.
(Other definitions for swarthy that I've seen before include "Dark-skinned" , "Dark skin" , "Dark-complexioned" , "Dark complexioned" , "Having a dark complexion" .)