[Drake]

Marines (MFR) use the LAND version of the CIRAS, not the MAR version.

The choice of flightsuits over MarPat/MCCUUs stems from the mission; flightsuits (Nomex) are typically used for CQC and other missions were flash protection is mandated. And as with other SF, depending on their objectives sometimes they'll want to blend in with the rest of the troops, sometimes they won't.

The CIRAS is used for maritime operations as well as blackside operations (blackside = expected direct contact with enemy). The PACA + MBSS or RRV configuration is also used (I've used it, it's very comfortable). MFR get issued the whole array.

As for the pics, most of the Marines you'll see not wearing the usual issued vests (IBA, MTV etc) are MEU, MFR, FAST (I've seen pics of FAST using black vests, as well as CB FSBE AAVs). Marines have a much looser structure than other military branches, and as such can be difficult to identify. You'll notice they don't wear patches, unit identification and on the field usually not even rank.