If you look at the art work for the Steel Legion; and this picture is one of the reasons I chose Steel legion as my guard, you will notice that their helms etc is a very brown burnished steel rather than a typical steel colour. In my mind this is both a perfect compliment but at the same time contrast to the khaki coats.
I chose the following colours to replicate this, Vallejo Model Colour Black, Reaper Master Series Scorched Metal and Reaper Master Series Aged Pewter.
Started off with a basecoat of 50/50 Black/Scorched Metal, this basecoat is only thinned so it can me painted on without leaving brush marks, easy way to test this is have a little undercoated sprue.
The first layer is a mix of Black/Scorched Metal/Aged Pewter at a ratio of 2/2/1, I thin this so that it becomes almost a glaze. In order the tell the right consistencey pull some paint up the side of the pallette well and the paint should flow back into the well leaving only a residue on the side. When painting these layers my brush strokes are towards the top edges of the armour.
Next layer is another drop of Aged Pewter into the previous mix at the same consistency focusing on the most light exposed areas
Further drop of aged pewter again same consistency using the same light principle
Final stage is a very watered down Aged Pewter painted on to the top edges in an edge highlighting style
Hope this helps, if you need any help let me know.