If it was my army, I'd go for white - but the more formal pure white with badge, brass bits and bobs etc, as opposed to the stained version seen in Zululand. This is purely based on aesthetics, as I think this is the smartest version of "tropical" kit. However, if it was purely down to UV absorption or whatever in a non-tropical environment, then surely the home service helmet would be used? Dark, very smart and very "British"

As to James' red-brown suggestion, that's actually very intriguing. How about a full red-brown uniform - a Martian "khaki" if you will. After all, if the dusty shade of khaki was practical for India and Africa, why not a local version for Mars? Grey was used in Ashanti and Sudan, so there is a precedent for a colour other than khaki to be used.
But.... it
is your Mars after all, so whatever you decide looks best in your campaign context is the right choice
