Knows how army kit is: primarily this colour (5)
I believe the answer is:
khaki
'this colour' is the definition.
(I know that khaki is a color)
'knows how army kit is primarily' is the wordplay.
'primarily' suggests taking the first letters.
The first letters of 'knows how army kit is' is 'KHAKI'.
(Other definitions for khaki that I've seen before include "Military hue" , "military material" , "Dullish brown colour" , "Military camouflage colour" , "Drably coloured" .)