The stripes are yellow, and are about the exact same tone and tint as the yellow
clickable smiles seen on the new board here. These where used for recognition to
identify the submarine as being in work up training. I have seen these on models
representing Type XVIIA & XVIIB, XXI, XXIII boats operating in the Baltic
training areas. Many modelers of German submarines of the types mentioned
above have found them useful also for better visibility when operating their model in pond
water without digressing from scale appearance. These German yellow stripes
would not be worn while conducting operations against enemy forces.
The US Navy used to paint the boat's contract hull number on the sail if the boat
was in port and/or conducting training or of a new skipper I was once told.
Operationally though, the name and hull numbers on US subs would always be
painted out without exception. Today, plastic sail numbers on the sail with magnets
attached are used in port so it is easier for new officers and crew to report duty to
the right address. No need to paint then, just pull off and attach again at the next
port of call.