In addition, the Army in Halo Reach usually wore olive or light brown fatigues with light brown armor, while the Marines wore gray fatigues with dark brown armor.Actually if you go to
I post every single camouflage pattern that shows up in halo Reach and halo CEA
Yeah, that's basically what I said. The Army typically wore olive or light brown fatigues with light brown armor (except for some special soldiers, who had green), and the Marines had gray fatigues with dark brown armor.
You can't really point towards Halo CEA as a solid source for Marine BDUs, considering how many corners were cut when it came to visual assets. Just like how the MA5C and M6G models were simply ported over as stand ins for the MA5B and M6D, it's likely that the team, for one reason or another, simply ported over the Army soldier models. Perhaps, since no "normal" Marine BDU existed (the Marines in Reach wore a vacuum sealed variant, judging from the sealed helmet and collar), it was easier to use the Army BDU, which possibly had a "base" variant available, given the large amount of variants seen in Reach. Hell, if you compare their coloration, the BDU seen in CEA seems to be half way between the Army BDU and the Air Force BDU from Reach.
I imagine most people know that the BDU seen in Halo Reach is clearly meant to be a re-imagining of the original Marine BDU in Halo CE, so the fact that the Marines in CEA do not have the classic coloration further points to this being an error. This goes even further when you consider that the Marines in Reach wore a unique shoulder configuration, while in CEA, this is nowhere to be seen. Considering that these Marines did not appear in the game until the player neared the Autumn, I think it's relatively safe to say that these Marines came from the Autumn, so there's no reason why we wouldn't see this BDU in CEA.