Copy that then. The texture is controlled in the Game \Data \Roster \German \Submarine folder in the various NSS_SubName.cfg files, such as the IXD2 here:
[UnitClass]
ClassName=SSTypeIXD2
UnitType=200
AppearanceDate=19420307
DisappearanceDate=19460212
DisplayName=Type IXD2
[Texture 1]
TextureName=data/Submarine/NSS_Uboat9d2/NSS_Uboat9d2_T01.tga
LightmapTextureName=data/Submarine/NSS_Uboat9d2/NSS_Uboat9d2_O01.tga
StartDate=19300315
EndDate=19450515
Frequency=1
[Unit 1]
Name=U-178
DOC=19420910
DOD=19450501
The Game \Data \Submarine \NSS_SubName folder holds the actual texture files. Note that the cfg is calling on the T01 file, but there are two others, slight variations, in the folder. The OM files are 2048x2048 pixels, while the stock files are 1024x1024, and slightly lighter in color. None of them are "black", but a combination of dark and light greys. Check your MODS and mod folder structure, and make certain everything went where it was supposed to. Maybe you are seeing "black" from a lack of any skin at all??
This is what the DW IXD2 T01 file looks like:
This is what the Stock IXD2 T01 file looks like:
btw - Imgur has changed their web site, and it looks like they are turning into another PhotoBucket... sigh