Flag officer for three-quarters of an hour (6)
I believe the answer is:
colour
'flag' is the definition.
(colour can mean a national flag)
'officer for three-quarters of an hour' is the wordplay.
I cannot quite understand how this works, but
'officer' could be 'col' (short for colonel) and 'col' is found within the answer.
'of' could be 'o' and 'o' is found within the answer.
The remaining letters 'ur' is a valid word 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 colour that I've seen before include "Blue or green, say" , "Complexion - pretext" , "Pigment, paint or dye" , "See 10" , "Hue, tint" .)