Whisky displays first sign of a hangover? (3-4)

I believe the answer is:

red-eyed

I'm a little stuck... Click here to teach me more about this clue!

'sign of a hangover?' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?

'whisky displays first' is the wordplay.
'whisky' becomes 'redeye' (I have seen 'cheap whisky' mean 'redeye' so perhaps 'whisky' could also mean 'redeye').
'displays first' becomes 'd' (1st letter of 'displays').
'redeye'+'d'='RED-EYED'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app