matthewv said:
There are currently no tutorials for terrain "skinning". The only terrain reskins I have seen on these forums are the
Blue marble terrain mod,
Hell mod, and
Song of the moon mod. (I did the terrain graphics for the Song of the moon mod)
If you want to reskin terrain the first thing you will need to do is unpak the art files. You will find the .dds files the are used for terrain skins in the art/terrain/textures folder(IIRC).
The Hell Mod thread is actually here. But thanks for the plug

You terrain graphics for Song of the Moon inspired me. Awesome job on Song of the Moon's terrain.
Originally, I was playing around with doing an undersea mod, or perhaps acquatic civilizations on Enceladus; but such a project would require a totally new set of unit models (not just reskins) for merfolk, intelligent squid and what not... also I was having trouble trying to make the terrain look like it was underwater since I would need some kind of flowing distortion effect over the whole visible map.
I found that reskinning terrain is actually much easier for me than reskinning units. Just grab the .dds files, export them to photoshop, modify them slightly, import and you are done. You can get a lot of different looking terrain just by changing the colors but not the geometry.
Another problem I was going to have with an undersea mod would have been trenches. That would involve a change to geometry, though maybe you could hack something up with modifying coasts.
I ended up modifying a lot of different .dds files to make the sea of fire, but I suspect many of them aren't being used. I suppose I should dig into the XML and figure it out.
Getting the colors to be complimentary is the tough part. I've had some really ugly orange and red terrain.
I think a Red Mars terrain would bretty easy to do and could be a pretty quick reskin of the Song of the Moon terrain. +trenches. Adjusting brightness/contrast, as well as adjusting the color range (shadow, highlites, medium tones... yellow-blue), and color replacement can take you very far.