BBC, Thailand: Brown Receiver; Composite or Trick of Light on M-16?

My nephew, Nick, had a BBC newscast on about human smugglers in Thailand.  It appears that the BBC is a bit less shy about showing weapons than many U.S. outlets, but that could simply be perception on this one show.  I watch very little TV.    From BBC.com:

Manit told us his district had long been used by human traffickers to transfer migrants from boats to trucks. He wanted to stamp it out. But he was getting little help from the central government, or from local law enforcement.

 The BBC correspondent was allowed to join a patrol off the coast.  In the video we see what appears to be an M-16A2 with a composite receiver.  If you look at the closeup of the receiver, it does not appear to be aluminum, but maybe it is just a trick of the lighting. 


 

Could it be that the lower receiver is a very worn lower that was cannibalized from another rifle?  The wear on the reinforcing seem typical of a worn receiver, but the color does not look  like the color of the upper receiver or magazine, or for that matter, like aluminum with the anodizing worn off.

A retired Marine friend tells me that some of the early M16 receivers turned brown with hard use, because he had one that had done so.  That is likely what we are seeing in this picture.   A very early, worn receiver that has turned to a brown tint, rather than a stray composite receiver. 

I do not know of any military that uses composite receivers for the M16 and its variants, but I would be happy to be educated.

The bright flotation devices indicate that no firefights are anticipated.  I suspect that the color is closer to orange than pink, so there may be some color distortion in the screen shots.

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Update:  From Archy on Freerepublic:

Has anyone else come across early M-16/ AR-15 receivers that wore/faded to a brownish tint? 

  When I worked at NWSC Crane in the early 1980s, we reworked some 25,000 very well-worn former USMC M16A1 rifles and refinished the lower receivers with a high-temperature, high-adhesion graphite-based finish. After a year or so of being repeatedly oiled [especially if 2-cycle oil or transmission fluid was used] they did indeed pick up a muddy chocolate colouration.

That rifle in the pic's fairly interesting because it's an early M16A1 [or XM16!] lower receiver upgraded with the heavier barreled M16A2 type upper. It could be that the user has a source of M855 ammo meant for the M16A2/M4 [which doesn't work too well in the 1:12 twist barrel of the M16A1/XM177E2] or it could simply be that the original barrel either wore out or got bent.
My AMVETS post has two unanodized M4s with VERY shiny lowers, and to which I've fitted 10-inch stainless steel bayonets- all for parade duty for our honour guard. The rifle in the pic hasn't been so polished, but looks to be a pretty good match for magazines that have lost their protective coating after a decade or two of use.