IIRC, there is in fact a specific texture used by XOF's UTH-66 choppers in both GZ and TPP. It's a two-tone paint scheme, with normally a black scheme acting as the base color and a silver-gray underbelly beneath. (Though from what I saw in TPP's prologue, there was an XOF gunship that a gray-gray combination scheme, so perhaps it's also colorable.)
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