Black attire, we hear, for early part of day (7)
I believe the answer is:
morning
'early part of day' is the definition.
(beginning of the day)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for morning that I've seen before include "Period up to noon" , "Time between dawn and noon" , "First part of day" , "Flower closing in the afternoon" , "early part of day" .)