Such a person does not necessarily look sad (4-4)
I believe the answer is:
'such' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'a person does not necessarily look sad' is the wordplay.
I cannot really see how this works, but
'look' could be 'eye' (eyeing is a kind of looking) and 'eye' is found within the answer.
'sad' could be 'blue' (similar in meaning) and 'blue' is found in the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for blue-eyed that I've seen before include "Specially favoured, probably blond" , "Such a boy is favourite" .)