Alternative take on the Imperial Fists.

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

1. Prime with Chaos Black
2. Prime over that with Leadbelcher

Silver (Armour Trim)

1. Drybrush with Leadbelcher to even coverage
2. Shade the recesses with Nuln Oil
3. Highlight the edges with Stormhost Silver

For grenades, replace Nuln Oil with Athonian Camoshade

Yellow (Armour Panels)

When I originally tried this scheme I put the yellow directly over the dark silver but this required 5 thin layers to get full opacity. I would recommend covering the areas you want to be yellow with a thin layer of Celestra Grey

1. Base with Averland Sunset
2. Shade the recesses with Agrax Earthshade
3. Highlight the edges with Yriel Yellow
4. Highlight fine points and sharp edges with Dorn Yellow

Blue (Cloth)

1. Base with Kantor Blue
2. Shade the recesses with Nuln Oil
3. Highlight the edge with Caledor Sky
4. Finer highlight along the edges with Teclis Blue

For gems, I added an additional extreme highlight of Baharroth Blue

Black (Armour Ribbing)

1. Base with Abaddon Black
2. Highlight the edges with Eshin Grey

Brown (Leather)

1. Base with Rhinox Hide
2. Shade the recesses with Agrax Earthshade
3. Roughly highlight the edges with Skrag Brown
4. Finer highlight along the edges with Ushabti Bone

Purple (Lenses)

1. Base with Xereus Purple
2. Shade the recesses with Druchii Violet
3. Layer the middle with Genestealer Purple
4. Fine point highlight of Pink Horror

Horns

1. Base with Rakarth Flesh
2. Layer upper two-thirds with Skrag Brown
3. Shade over with Agrax Earthshade
4. Highlight with Rakarth Flesh
5. Finer highlight with Pallid Wych Flesh
6. Tip the points with Abaddon Black