Just to cloud the issue a little more:- I had a look at the catalogues in the library, no 1936, but the 1935 model had a black tank with purple panels – no mention of a diamond on the top and no mention of coloured lining.
The 1937 model had a choice of a black tank with white lining or a black tank with purple panels – no mention of a diamond or the colour of any lining.
In my garage , I have a mid thirties tank, black with purple side panels and white lining but no diamond on top. Also I have a Clubmans Special tank, black with purple panels and diamond, all with white lining.
You pays your money and takes your choice it seems!