Dark clothing not universal early in the day (7)
I believe the answer is:
morning
'early in the day' is the definition.
(I've seen this before)
'dark clothing not universal' is the wordplay.
'dark clothing' becomes 'mourning' (mourning can refer to garments worn in mourning).
'not' indicates named letters should be taken away.
'universal' becomes 'u'.
'mourning' with 'u' removed is 'MORNING'.
(Other definitions for morning that I've seen before include "Flower closing in the afternoon" , "First part of day" , "Forenoon" , "Before lunch?" , "Time between dawn and noon" .)