^ The actual difference between colours in that sort of climate would be minimal at best, that particular primary school science lesson is often drawn out to make conclusions which are a bit too sweeping. Far more important is what the material is - and it's likely that's all he had with him that was vaguely suitable. And wearing a black cap is better than no cap in desert sunlight. And stripping down in desert sun? bad plan. You want to cover as much skin as possible - and they're on water rationing, they don't have the luxury of pouring it over themselves.
