First thing first. I can not stress this enough. PRIME YOUR MODEL. Any model from a standard Marine to a pricey model such as a Contemptor deserves to have a good and solid foundation for the paint to be applied to them.
I have heard many arguments as to which primer to use. I will give you my opinion.
IMHO Army Painter primers are some of the best. For those on a budget Krylon Primers are also good but can be more prone to giving a Grainy finish.
I chose to prime my model in Army Painter Black.
The next step is to apply your Base color.
I chose for my Grey Knight Contemptor to use Mithril Silver
Be sure to use this color sparingly, Metallic's go very far. Just be sure to get a thin but solid coat of color on your model.
The next step is to give your model some depth and another color.
For this i use my standard Grey Knight wash. The wash is a 1:2:1 mixture of Water: Azurmen Blue: Badab Black
Mix this well and apply to your model LIBERALLY! be sure not to allow the wash to pool on the flat portions of the armor.
Now. I went ahead and sipped a step with my smart self. The next step is to Drybrush the silver back up on the model. This will leave a blue tinge to the armor but brighten it bu a bit more.
in the following pictures you will see the finished product.
For the knee Pads I simply taped it off and painted it. I then carfully went and fillled the other half with a 1:1 mixture of Fortress Grey and Skull White
The reds where done with a simple step up from Merchrite to Blood Red.
The Parchment was done in Deneb Stone then washed with Delvan Mud