Captain Lehmann - The hand-drawn ship icons are as I said before in an earlier post, all in the /data/Sea/N_Blah folders. They are usually called NBlahnameofship_Shp.tga.
All you have to do is invert the colours in photoshop and save. It works properly for me in the Improved U-boat version.
The question of what file controls the definitions for the colours was the reason I started the thread, if you read the first post again.
It could be one of the .dat files, but I don't know which one. My concern was the sonar lines are black with the IuB mod along with contact tails etc, but you're probably right in that its not too bad and forces you to pay more attention to what your SO is saying.