Ryandor.com

I've been working on UO maps for a couple years now but have never delved into this topic. I've seen pictures of a few shards using things like brown mountain terrain, and I can easily see a few useful applications for some recolored (the art itself, not hued ingame) tiles on my map. My question is; how does one extract the terrain art from whatever mul it is kept in, and then how would they add the recolored tiles back in?

I have some experience with verdata editting so I'm not asking for someone to write a huge tutorial. A point in the right direction would probably be enough.

Thanks guys.