-MAD- Sarge is right. A rule of thumb is to follow the "light vs dark" approach. To lessen confusion, a dark shirt would be with green, while lighter shirts would be with tan.
Don't wear a black shirt with *insertcolorhere* pants. Don't wear white/snow/urban/navy camo... at all.
Follow the green vs tan approach and you will be just fine. Keep in mind, plate carriers and vests don't count. Just pay attention to your pants and shirt/hat.