One reason you see mixed camoflage, is because some units haven't recieved some items in the appropriate color. When I deployed to Iraq the first time, we had DCU's, but Woodland IBA's. At that point in time, the army was'nt issuing Desert body armor. They're just now catching up. Also, it does help to mix it up a little. Like, if you have a mission in northern Iraq, where there's some mixed vegetation, it might help to throw in some woodland, or green.