I've just had a reply from
Prinz Eugen E-Boat Site
"Hi Ian
Thanks for the note. I've always associated the yellow rubberized maps with Luftwaffe use, however its interesting that this one would be so detailed as to water depths, and buoys, and not be LW marked.
About the only piece of definitive information I can give you, is the yellow color was intended to illuminate the map under UV light, leaving the rest of the cockpit in darkness. I don't know if Schnellboote would have UV lighting in the navigation cabin, its an interesting question though! I'll keep it in mind in my research.
Sorry I couldn't be more helpful.
Sincerely,
Dave"