Although the Canadian Armed Forces are a single service, there are three similar but distinctive environmental uniforms (DEUs): navy blue (which is actually black) for the navy, rifle green for the army, and light blue for the air force. CAF members in operational occupations generally wear the DEU to which their occupation "belongs." CAF members in non-operational occupations (the "purple" trades) are allocated a uniform according to the "distribution" of their branch within the CAF, association of the branch with one of the former services, and the individual's initial preference. Therefore, on any given day, in any given CAF unit, all three coloured uniforms may be seen.

What is the fourth similar environmental uniform?