So I'm a little late jumping on the devlan mud bandwagon, so i'll hold my remarks of amazement.
I had some chaos hounds that weren't painting themselves (actually figgy's), so i gave them a gray undercoat and attacked them with washes without even using a base coat of colors. Just wash right over undercoat.
After one application the result was unimpressive, but i stuck with it and applied several more coats, and picked out the details.
Undercoat: light gray spray (got a little fuzzy, but it ended up looking ok)
Skin: 2-3 washes of Orgyn flesh
Fur: 3-4 washes of badab black or devlan mud
Mouth/tentacles: leviathan purple wash and/or glaze
Scales,eyestalks, etc: thracka green wash and/or glaze
Teeth, horns, spikes, claws: faint glaze of bone in several layers
Final step over all: Watered down black wash, dove gray drybrush (folk art acrylic paint)
The pictures are washed out i apologize...
Also i have this very early stage skaven, done with a devlan mud over a white undercoat with dwarf flesh glazes for the skin.