If you want them to be bright and vibrant, then you should make sure the wash flows only into the recesses, without staining the main color of the Skinks. An easy way to check this is to give them a good coat of gloss varnish before you apply the wash - it won't stick to the surface as well, and it will pool up in the recesses.
And if you want to keep it bright, then I also recommend Gryphonne Sepia. It's a much more lively color than Devlan Mud.