Just some thoughts on Contrast. These are some of the things I did with washes and inks years ago. Apologies for the bad photos but they are gloss varnished and not the easiest thing to photograph with a phone.
I think what GW have done is get a transparency somewhere between an ink and a wash. The top picture is wraiths done with purple ink and the contrast between shade and highlight is more pronounced on the GW stuff. The bottom is just a green wash and the contrast is greater than the GW stuff. The photo in the middle was done by dry brushing a black base coat with white then giving it a green wash.
One thing Contrast will really show up is mould lines and flaws on the models.
