This mod uses the dark terrain art files from the Warlords Vikings scenario. For merging, just drop the art folders and files in your own mod. It should be compatible with all civ versions and patches.

http://img363.imageshack.us/img363/7366/civ4screenshot0109zg1.jpg

Download: http://forums.civfanatics.com/downloads.php?do=file&id=10202

You don't need to copy all the art files. Just a modified Civ4ArtDefines_Terrain.xml and Civ4ArtDefines_Feature.xml that points to the dark files in the Warlords install will accomplish the same effect. Then you won't have to distribute Warlords art assets.

I was wondering: what if you don't have Warlords installed? Is all the Warlords art included in BTS?

I never knew that scenario came with custom art. In my opinion it looks a lot like blue marble but with less detail.