I did the battle damaged armour 'damage-in'. Basically, you paint the metallic damage first and then paint in colour of the armour panels 'inside' the damage. I use the same method for tanks, orks, etc.
1) Primed Black
2) Whole model drybrushed old Citadel Boltgun Metal, then lightly drybrushed Citadel Necron Compound.
3) Interior of the armour panels painted Citadel Mechanicus Standard Grey
4) Interior of the armour panels lightly highlighted with Citadel Dawnstone.
5) Gloves and armour seams basecoated Privateer Uniform Green. Helmet cables basecoated Privateer Bastion Brown.
6) Weapon basecoated old Citadel Catachan Green.
7) Whole model washed with OLD Citadel Badab Black, thinned with NEW Citadel Lahmian Medium.
Highlights and details are as desired based on the colours above. Brotherhood insignia freehanded using Citadel Skink Blue, highlighted with the really light blue Citadel Edge paint (Can't remember the name).
Hope that helps!