This is my first attempt at a Militarum Tempestus Scion. I deliberately chose the Tempestor, as he is one of the few models in my small force that has an unobstructed chestplate.
At first, I undercoated the model with Halfords Grey Primer, and then basecoated him using 'The Fang' - the Citadel Spray Paint. I was worried that I had made him too blue, initially, but the more detail I added, the lesser the effect - which was good.
A simple pallette of blue, brown, grey and silver should mean that these guys are relatively easy to paint, whilst also having a distinct look to them.
I used Vallejo Gun Grey (which is a muted, lead-style metallic) for the main metal plates and weapons, and then I picked out the highlights in silver.
I used greens (Kabalite Green and Moot Green) against an Incubi Darkness base for the lenses and electronics to create a little contrast. I think it worked!