Colour of military uniforms (5)
I believe the answer is:
'colour of military uniforms' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for khaki that I've seen before include "Military fabric" , "Drab military colour" , "'Colour, often used for military uniforms (5)'" , "Yellowish brown (used by military)" , "Drably coloured" .)