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

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

Gold (Armour Panels)

1. Base with Retributor Armour
2. Shade the recesses with Agrax Earthshade
3. Highlight the edges with Stormhost Silver

Blue (Armour Trim)

1. Base with Caledor Sky
2. Shade the recesses with Nuln Oil
3. Highlight the edges with Teclis Blue
4. Highlight fine points and sharp edges with Lothern Blue

Blue-Green (Details)

1. Base with Sotek Green
2. Shade the recesses with Drakenhof Nightshade
3. Highlight the edges with Temple Guard Blue

Silver (Metallic Details)

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

For grenades, replace Nuln Oil with Athonian Camoshade

Light Grey (Cloth)

1. Base with Celestra Grey
2. Shade the recesses with Drakenhof Nightshade
3. Highlight the edges with Ulthuan Grey

Black (Armour Ribbing)

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

Brown (Leather)

1. Base with Rhinox Hide
2. Roughly highlight with Skrag Brown
3. Finer highlight with Ushabti Bone