A little late to this party, but:
most events are structured tan camos versus green camos with each side having a list of common camos to select from. So, for example, if you want to play on the tan side, you can't go wrong owning a set of DCUs, Arid MARPAT or Multicam. Likewise, for the green side, M81 woodland, temperate MARPAT, OD, etc.
It gets more complicated once you start to talk about the bigger national events - these may have much more specific camo requirements.