I believe that best high rez and graphical u-boat interiors are incorporated into GWX.
However, if your graphics are 'washed out' then try adjusting your gamma settings. I will admit that my u-boat interiors are very bright/colourful, not indicative of the inside of a control room but I put that down to having a very bright LCD monitor.
These u-boat interiors were released as a standalone mod BUT you will not find them anywhere as they have been removed.
Anyone for a donut????