Hi there Ive just built one, Im now working on the last Darnell kit type XX1 and I have a built Robbe u47, Ive been told that the U99 was all over grey, or rather they all were, it was only when they had a refit that the bottom half of the hull was dark grey, i guess it depends on what you want, on training they where grey all over and had a yellow band round the conning tower I think, ive done mine twin light and dark grey but I dont think she was ever that colour scheme, the robbe kit is twin but all the wrong colours, so im putting that right in the next few weeks, I think you can get cumualnimbus grey ( spelling wrong :-) which is the closet, bear in mind the real paint jobs where a mixture of greys and was never evenly put on, lets face it who worried about the paint job in the atlantic :-) Id go for over all grey, does look nice though twin greys