The Luna Wolves, and their later incarnation as the Sons of Horus, are one of the First Founding Space Marine Legions who get a lot of attention from pre-Heresy fans. Despite this, there is little by GW by way of a guide to their appearance. As the Sons of Horus, who I have chosen to paint my members of this Legion as, we’ve got no officially-painted miniatures and a handful of textual and artistic references.
This thread contains a tutorial describing how I paint Sons of Horus. This isn’t by any means the only way, or a more official method than that of, for example, Sotiros or Iacton, but it is my way. My inspiration comes from the illustration in the
Index Astartes article and a handful of references to the armour being a ‘metallic sea green’ in colour.
Here I’ve painted one of the classic Mark III ‘Iron’ armour models, with a plastic oath paper (purity seal) glued onto one shoulder pad. In hindsight this may not have been the best choice, as the casting is quite old and some detail is eroded, but hopefully you’ll agree that the method works well enough. It’s also quite fast, so you can assembly-line the painting to a reasonable degree.
Anyway, on to the pictures! (Camera’s not great, but I’ve done my best.)
1. Prime the model in black. Inclement weather means I did this by hand, but I’d recommend a spray primer for a smooth finish.

3. Basecoat the armour with Dark Angels Green. I used a tank brush for this; it doesn’t have to be near.

3. Now we’re into highlighting. Mix about 1:1 Dark Angels Green and Mithril Silver and heavily drybrush the armour. After this, drybrush a further highlight with almost pure Silver. If you have more time or patience you could either paint layer highlights or use more shades when drybrushing, but I like to be quick. The model should look more silvery at the end of this stage than you want it to when finished. Tank brush time again.

4. And now some shading! I use an approximately 1:1:1 mix of Dark Angels Green, Dark Green Ink (try Thraka Green with the new washes) and Blue Ink (try Asurmen Blue), slightly thinned. Apply a thick coat over all the armour to deepen the colour. Sometimes I apply a second wash of this, if it is still too pale. Tank brush time again, again.