Clue: Peacekeeper's unhappy with king eating vegetable? On the contrary! (4,5)
Answer: BLUE BERET
Explanation: Peacekeeper's unhappy with king eating vegetable? On the contrary! (4,5)
A charade of BLUE ('unhappy') plus BERET, an envelope ('eating') of R (*Rex*, 'king') in BEET ('vegetable'), with the function of the particles reversed ('on the contrary'); for the UN peacekeeping military.