Based on Sezrion's work on the 40k Homebrew site.

The main colours are red, black, and corroded brass.

General Information:

My general method is to lay down all the base colours for the model, then do all the shading in the recesses before moving on to the highlights.

I don't own an airbrush, so the recipe will mainly consist of brush on paints.

Priming:

I find the metallic sprays from GW tend to be a little on the transparent side, so an initial undercoat of grey helps.

1. Prime the model lightly with Mechanicus Standard Grey
2. Prime over that with Retributor Armour

Brass (Armour Trim):

I generally start with the armour trim so that any time I get paint on another piece its easy to cover later.

1. Drybrush lightly over the model with Retributor Armour to even out the colour
2. Shade the recesses and around any rivets with Agrax Earthshade
3. Add small amounts of thinned Incubi Darkness around rivets
4. Highlight fine points and sharp edges with Stormhost Silver

Red (Armour Panels - Arms, Legs):

1. Base with Khorne Red
2. Shade the recesses with Agrax Earthshade
3. Highlight the edges and along the inside of the armour trim with Evil Sunz Scarlet
4. Add fine points of Kislev Flesh

Black (Armour Panels - Hands, Chest, Shoulder Pads, Backpack):

1. Base with Abaddon Black
2. Highlight the edges with Eshin Grey
3. Highlight fine points with Dawnstone

Green (Details - Cloth, Wraps, Eyes):

1. Base with Incubi Darkness
2. Shade the recesses with Nuln Oil
3. Highlight the edges with Kabalite Green
4. Highlight fine points with Sybarite Green

Grey (Details - Armour Ribbing):

1. Base with Mechanicus Standard Grey
2. Shade the recesses with Nuln Oil
3. Highlight the edges with Dawnstone

Brown (Details - Leather Pouches):

1. Base with Rhinox Hide
2. Shade the recesses with Agrax Earthshade
3. Roughly highlight the edges with Skrag Brown
4. Add a fine highlight of Ushabti Bone

Silver (Details - Weapons, Backpack Arms):

For grenades, replace Nuln Oil with Athonian Camoshade

1. Base with Leadbelcher
2. Shade the recesses with Nuln Oil
3. Highlight fine points and sharp edges with Stormhost Silver

Blue (Details - Power Weapon Effect)

1. Make a long, jagged line using Sotek Green
2. Shade around the power unit using Drakenhof Nightshade
3. Layer the middle with Temple Guard Blue
4. Add a fine line of Baharroth Blue
5. Add points of White Scar