I've seen the real poncho, at the Leone exhibit at the Western Museum about 6 years ago. It definitely is a greenish-brown, more like in-between, depending how the light falls on it, and different surfaces have slightly different shades.The poncho and other related memorabilia there belong to Eastwood, who loaned it to the exhibit, along with the pistols, boots, etc.
Some nice shots here!http://hollywoodprop.com/ouatii.htm