This is my recipe for Sons of Medusa space marines. It seems like a lot of step however airbrushing makes it very quick.

Power Armour Recipe

1. Base coat models in Chaos Black
2. Coat entire model in Dark Angels Green
3. airbrush from a flat angle in Scorpy Green
4. airbrush from above at a 45 degree angle with Light Livery Green
5. airbrush entire model Hexwraith Flame

The Hexwraith Flame flame is used at this stage as a psuedo wash on the models. It seems to darken it up, but when the next two steps are completed it adds shadows and brightness to the model.

1. Repeat steps for Scorpy Green and Light Livery Green
2. Top down airbrush Sun Yellow

Helmets

1. Base coat :Citadel/GreySeer
2. Wash with Apothecary White
3. paint with Grey Seer and touches of White Scar