I recently added a 5-man meltagun support squad to my Horus Heresy Alpha Legion army. I chose to use MkIII armor for aesthetic reasons; I think the heavier look of the armor lends itself well to squads armed with shorter-range weapons like meltaguns.
My process for this color scheme is straightforward; I base in a metallic silver, and then follow up with light coats of Minitaire Ghost Tints. Blue first, and then Plasma Fluid on top of that for that great Alpha Legion color. Here I chose to also use the airbrush to do the dusting on the legs, rather than a paintbrush. I think the effect worked really well. The dark coloration on the gun muzzles is done with Secret Weapon Miniatures’ Exhaust Black weathering pigment.
Interested in having your own Horus Heresy Legion painted? I’m open to doing painting commissions! Please get in touch at firstname.lastname@example.org with the subject line “Greyed Out Painting”.