Hi all thanks for the kind words
Hocking Hellgrau 50 was often used on pre and early war boats then Dunkelgrau 51 was also used alot, there are also a number of other colours which were used.
As regards to the lower hull my research points to Schiffsbobenfarbe III grau (Dunkelgrau 53 was the same colour but did not contain any anti-fouling ingredients)
check this link out
http://uboatcolours.mysite.wanadoo-members.co.uk/
hope this helps.