I believe blue lights are post war, as far as I know, U-boats were fitted with red and white only. Both red and white in the control room and tower, white only throughout the rest of the boat.
I've never seen blue lights used in U-boats, and to my knowledge, this is a modern practice (as red was found to have the opposite desired effect on the eyes).
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"I must confess that my imagination refuses to see any sort of submarine doing anything but suffocating its crew and floundering at sea." - H. G. Wells
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