I'm assuming you mean camo and not dress uniforms(soldiers can have several uniforms). Its all about location. Where are the men going to serve? In green plains? Forests? The desert? Depending on where the soldier is going to fight they are issued the uniform that best helps them blend into the environment. Camouflage is all about making it harder to be seen, and shot. Edit: I'd like to expand on my comment. Even now camo uniforms aren't all tan. Although, the tan uniform has become far more common (at least in the U.S.) because the recent wars in Iraq and Afghanistan where a tan camo would be of more use. In the past there were many more green uniforms because the U.S. fought in places like Vietnam and the Pacific islands (heavily forested, much greenery). Also there had been fighting, and the expectation of fighting (the cold war), in Europe where large green fields of grass and some green woodland are common.