They have gunmetal power armor so you can use whatever slightly dark metallic paint; probably GW Leadbelcher, Vallejo Game Color Gunmetal, Vallejo Model Air Gun, or something similar.
Their shoulder pads are black with dark green trim so any black will work and whatever dark green you want; GW Caliban Green would be a good place to start and just highlight up from there.
As far as the chapter icon goes, you could use the skull transfers that come in a space marine tactical squad and it would look just fine. Your other option is to freehand them.
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