Interesting, I would have thought China or India for this piece before anything else although the selvages appear to have a double cord warp wrap.
The color difference is drastic. Some consumers would not pass this for anything more than just what it is: a color difference between the front or back. dyes probably play a large role in this, although general oxidation, subject to a lot of light as you mentioned could be a possibility. I don't know about a tea wash for this, although that's not out of the question.
as for the subtle look, it is desirable as long as it is not from dirt, and is very even. If some areas look more affected than others, that would be a problem. Also, some chemicals used may dry up the pile material and make is susceptible to premature wear and loss of pile. Not often the case, but something to keep in mind if it's a harsh acid bath.
For this rug, it would help a lot to see the pile parted like here in the first pic:
http://www.rugrag.com/po...ug-Moth-Infestation.aspx