Here he is. My Mortarion.
I set out wanting to replicate the Above artwork from the Horus Heresy artwork for the Card game. This proved to be quite difficult but I think I got close.
The Book Flight of the Eisenstein described Mortarion as having Brass armour under a Shroud of grey. I googled Brass and got many hits of this colour.
I decided to use a Vallejo Old gold to come close to this colour. The Old gold can look quite dirty especially after washed with burnt umber oil paints and white spirits :)
The cape is an off grey white with a selection of weathering Powders fixed and blended with White Spirits.