I found this very interesting too since to date I have never found out exactly what Dark Tarmac No.4 looked like. A Canadian contact says a very dark blue grey whilst many years ago it was reckoned to be almost black. Contemporary colour photographs taken from the web do seem to show the blue-grey shade. If I have read it correctly, I see that in the formuala for mixing there are small elements of yellow and red. These combined with black would give the finished colour a slightly green tinge. I would dearly like to see the sample mentioned in this document and compare it with some type of current standard. If, of course, the archivist did include it. (they often don't!) So much for the oft stated "wartime paint was made cheap wasn't it?"