Right, here's my test model for a plain old silver fist marine...
Black is the main colour, of that i have no doubt. At the moment the model is Black undercoat, drybrushed with a 50/50 Fenris Grey/Chaos Black. Planning on extreme highlighting with Adeptus Battlegrey.
Trim and helmet is iyanden darksun, covered with golden yellow and highlit with sunburst yellow.
Hands are Tinbitz covered with chainmail, a black inkwash, and will be highlit Mithril Silver. I might take it down to just one hand.
Bolter is so far just some Red Gore, and this is where i have the most misgivings. A) a red bolter makes him look like a McMarine. Red Gore works the best of all the reds but I'm still not sure.
Options are... different helmet colour, different bolter colour.