It's one of the original mount and blade textures that's all on one .dds file.
If you want your black greaves to look like the cased greaves you should probably just retexture the cased greaves instead of trying to retexture the black greaves to look like the cased greaves....in short retexturing the cased greaves would be easier......did that make any sense?
Also the only texture file I could find with the black armor was costumes_lod