The actual prop wardrobe used is a replica of Russian sniper ponchos. They are readily available on ebay, I would recommend getting one of those. It hangs better, longer and can be shaped differently than the Hot Toys mudtrooper cape. There are two colors a darker green and a graphite.
I have been dying both with Rit charcoal to achieve good coloring. The Russian poncho comes green so a little die goes a long way of getting that dark green color. A full dye gets a nice graphite color.
Straight from the troops. Always pick up interesting things of the costuming from these threads.
Linky ->
https://forum.mepd.net/index.php?/topic/15613-solo-mimban-trooper-crl-development/page/2/