Officer's hat -- brown with a touch of indigo inside (7)
I believe the answer is:
captain
'officer's' is the definition.
(I've seen this before)
'hat brown with a touch of indigo inside' is the wordplay.
'hat' becomes 'cap' (I've seen this before**).
'brown' becomes 'tan' (tan is a kind of brown).
'with' says to put letters next to each other.
'a touch of' suggests taking the first letters.
'inside' is an insertion indicator.
The initial letter of 'indigo' is 'i'.
'cap'+'tan'='captan'
'captan' enclosing 'i' is 'CAPTAIN'.
(Other definitions for captain that I've seen before include "Is Pat Cain in charge of the ship?" , "Army rank" , "Leader" , "American police officer" , "soldier" .)