I always found washes (or shades as they are called now) really useful especially for painting horde armies. In your introduction post you said that you want different squads to be painted in different clan colours. In that case I think that using Agrax Earthshade (which I guess is the one you are using) on all the cloths is a great idea because it ties the different squads together.
Concerning the waywatcher green: This is a Glaze and not, like e.g. Earthshade, a Shade. Basically what it does is, it makes the skin look 'greener' instead of shading the recesses. I haven't really tried it myself on skin painted the way you do it, but I know what you mean – it adds something to the model. It would help if you post a picture, though. I always love to see how Ork players paint skin.
Hope this helps!