I run a flecktarn uniform with OD gear, though either will work fine. Just go with whatever contrasts the least. Something to consider is how heavily your flecktarn is faded. My uniform is surplus from the '90s and it has taken on a somewhat brighter tone than the brand new stuff I'm mixing it with. This doesn't bother me, it provides a bit of countershading (
http://en.wikipedia.org/wiki/Countershading), but to keep this effect I need to avoid putting things on my chest that are darker than the shade of my uniform.