Wed Mar 09, 2011 7:10 am by xDreamerx
You should consider reading Jordans book. You can find the link here on this site somewhere lol Its good reading for beginners. I think questions like yours would benefit you to read it.
As for greywash, you can use it for anything you want. Coloring, shading, shadows, powder shading...etc. Its up to you as the artist on how to manipulate and control it. So there is no real rule set in place that says what you can or cant do with greywash....goodluck and have fun and most importantly be safe in this art form! !