You should be very wary of using any form of military kit-dyed or otherwise- in S America.
when you say;"some places do not like you wearing military uniform" well, lets just say that that is a massive understatement.
You may experience anything from being held up at customs for a while right the way through to- who knows?
Ok, so ray mears has been filmed with all sorts of green kit in the jungle etc-well yes but he's also in the company of maybe 10 other people from the bbc with local "fixers" tagging along to boot.
Most of the replies seem to have completely missed this point- in fact, you would almost certainly be better off consulting the "know before you go" government website and don't waste your time and money faffing on with dyes etc and just buy a couple of inexpensive cotton shirts-in my experience, the soldier 95 shirts are not all that good anyway, the underarms tend to start to fall to bits after a few weeks of tropical sweat!
don't want to put a damper on your trip but you really should go check out the site mentioned above for information on where ever it is you intend to visit.
R.B.