Well, first of all, it's not one color

To get nice transitions like that, you have to wet blend and highlight it for those light colors, and wash around the recesses for the dark colors. You can't get this type of effect solely by putting on a paint and washing it.
If you have an airbrush, you could paint all the Rakkarth-Flesh-ish colors (the tan armor plates) with an airbrush (and highlight it with one), doing the grey/black areas after. It wouldn't be worthwhile to mask, because there's just way too much to mask (you'd have to paint the grey parts by hand, after).
There are also some sharp transitions from almost-white to 60% or darker grey over only a couple of millimeters. Those are a challenge to achieve. You also have to edge highlight with white, or nearly-white, and that can also be challenging to do cleanly (especially when it is against a gradient, giving you no margin for error)..
I'm certainly not trying to discourage you from trying, and I think it's a very nice paint scheme. But achieving it at the quality of the picture you have is not for the faint of heart.
You could, of course, start by simplifying it -- instead of wet blending.. well.. everything.. just stick to layers and washes, and wet blend a couple of high visibility areas, like the shield on the shoulder and the wrist gadgetry.