This is an unmodified, partially painted, molded-color finish.
I wanted to give it a cold-climate feel with weathering, but it's a bit subtle...
I remember being very excited by the opening when I first saw "War in the Pocket." The GM Cold Climate Type got pretty beaten up, though. It's one of my favorite GM designs, so I was really looking forward to it being released as an MG (Master Grade) kit. (Sorry for bringing up something from so long ago.)

MG GM (Cold Climate Type) | ISAMU's Gunpla works