[Zideruic]

Actually it's pretty easy...you basically make a pallette of about...6-11 colors in a different shade of that gray you have there, imagine a source of light, and put the brighter colors where the light would reflect, and the dark areas where the light would least affect it...but then you need to have a fade from light, to dark, which is where the colors in between the darkest and lightest on your pallete come into the process, you simply blend the colors in between in a texture such as rough metal(the archor) by blending it with dots overlapping in each shade which makes it look rougher.