Boomerang is correct, the turrets on the Humvees would be manned constantly , your crew served weapons are used to provide security for the dismounts. So to be evn more accurate the weapons would be facing outward, and in your case specifically the M113 would be covering the 6 o-clock position (behind it down the road) and one of the Humvves would be covering the 12 o-clock position (in front of it up the road) as VBIED's (vehicle borne IED)are a huge threat, so covering the roads is important.
As far as the different colored parts go, in Iraq its not unsual to see Humvees with different colored body parts, tan and green, nothing crazy. Most new body panels come in green so whenever you Hummvee gets damaged (usually from IEDs) you end up with a mismatched vehicle. I suppose they eventually get painted, but ours never did, it would be a waste of time and paint, as they would need replacing soon anyway.