The color of the life ring was RED !! . Please see VOM ORIGINAL ZUM MODELL: UBOOTTYPE VII C by FRITZ KOHL / AXEL NIESTLE , page 49 here you will see an original wartime picture of a type 7 U-boat with the red life ring. What would be the sense of black ? you throw it to a drowning man and he cannot find it !!! or if you are floating around with it how do would be rescuers see you ? Type 9's were originally fitted with these rings ( I have pictures of this also ) but after a certain time period the life ring was deleted as it was seldom used and in many cases came off underwater during an attack ( not good if you are trying to hide from your enemy ) . I do also have pictures ( wartime ) of U-boats with wood color decks .