For the basis I used Codex Grey as the armour, I was trying to avoid the general silver marine which will be popping up everywhere. I originally had a darker grey for the gears but wasn't happy with the result and repainting them black like the 'Eavy Metal models. I also followed the guide to painting Grey Knights in White Dwarf but substituted the Metalic paints for various Greys.
For the Sword I used Chainmail with a very very light wash of Asurman Blue to try and give it a power weapon look
Again I took inspiration from 'Eavy Metal and painting my Heavy Incinerator with Gold tanks, these were based Codex Grey, with Shining Gold followed by a wash of Gryphonne Sepia, and topped with Burnished Gold. This gave me a pleasing gold look and compensated for the thinness of the Gold paints.
Laslty for the back, the only thing to really paint other than the gears and hydrolics (which are black) was the skull and cog symbol, which I painted half black half gold as per the Mechanicum. I also gave the exhausts Boltgun Metal with a Sepia and Baal Red wash to make them look hot and dirty... (that sounds so wrong).
Ignoring the seams and mould lines I am happy with this painting as for one, I am extreamly un-artistic and unable to hold a paintbrush steady, I also have no idea on colour co-ordination.