Hi Joe,
The reason to have PFD(s) and liferings painted in hi vis yellow, orange or red is not for better indendification by the sailor, who fell overboard, but rather for better visibility by those attempting to rescue him. Because once the ring was thrown the distance between the swimmer and the ring was much smaller than the fast disppearing ship/boat, which takes several hundert yards to turn around and pick the guy up. If no ring was thrown immediately when the guy goes overboard it will not be thrown several hundert feet later.
Front boats on patrol did not carry any ring topside, they were only brought up when entering port and in port - ready to throw to the drunken sod slipping on the gangplank or whatever. U253 on page 49 was during her training entering the port of Hela in the eastern Baltic. And yes, this ring is red.
Re: wood colored decks: pl note - the supply of teak and similar hardwoods was extremely limited particularly in the later war years. All other wood had to be treated with preservatives, i.e. painted. Otherwise it would have rotted very quickly.
Rgds, RB