You're talking about the Sideshow 12" figure. No one has done it yet, so I could approach the LMO about the possibility of approval since it's only on the one item. Let me know if you want to pursue it.
Actually, in most of the references the suits are considered shiny. it depends on the medium being used that will make it vary. As mentioned above, there are parts of the suits that may be flat black to help them pop a bit. Mainly helmet detailing, and the body of the thermal detonator. You should check out the CRL, to research color schemes and costume requirements.
-iz