I have at last managed to create a very close match to BS.33 & post war 633 RAF Blue Grey colour introduced in 1937 for most RAF ground vehicles. Some members might wish to know the formula.
Humbrol enamels:- 5 parts H32 dark grey + 2 parts H14 French Blue + 2 parts H33 black.
This colour is the correct shade for RAF vehicles, not Humbrol 96 which was intended as the RAF uniform colour. Please note too that the new Austin Utility vehicle should not be painted this colour since these cars were not used by the RAF.

... a very useful mix to have, and no doubt spot-on as always!

..by no less than a chap who actually used to put the paint on vehicles. He is restoring a vehicle now he has retired but collected historical material when he served in the RAF.

I have just been playing with this colour and Mike Starmer also suggested, back in January 2008, that Humbrol 112 Tarmac was an alternative way to get the right colour. Paint it on then add a coat of satin varnish and hey presto! RAF blue-grey. When I first used it I hadn't applied the varnish and a number of people, looking at the colour on an Airfix kit, agreed with me that it was far too dark. But a bit of varnish and.....wow!
Sadly Humbrol 112 is no longer made as a paint colour by Humbrol. It is actually very effective, if slightly alarming at first. Now I shall try this new hue for the 1/35th Queen Mary trailer unit that I am building, as seen in the late summer of 1940.
So is this a replacement for 112, Mike, or is it actually much different? Your previous Humbrol 'mix' for RAF blue-grey was given as 4 parts of 77 Navy Blue + one part of 67 Tank Grey, (allegedly equivalent to 112) although I currently prefer my last tin of Tarmac with a hint of 77 and a splash of medium sea grey. What amazed me was the change induced by just a thin coat of satin varnish. I assume that the varnish applies to the new mix as well?
Intriguingly, I have been looking at an old Queen Mary trailer and the owner has it currently painted in a much lighter colour of blue-grey. He matched that to the colour he found when he split the wheel rims. It is nothing like the colour of Tarmac, but after 60 years who is to say that the colour inside the wheel rims was original? My recollection of the RAF vehicles in the 50s and 60s is that their blue-grey was lighter than the Tarmac and closer to the RAF uniform colour or am I just imagining things?
My thanks to Mike for his continuing efforts to find out what these colours actually were, but please don't make me have to go back and repaint too much of my stuff!
John

Humbrol 112 was the best colour to my BS.33 & 633 samples when I first wrote about it. As the colour was not then a priority colour then H112 was very close for a 1/76 model. My 77+ 67 mix was a next best. But recently when trying a serious reformulation I discovered that 77 is made with Prussian blue that has a green element which cannot be eradicated. Humbrol habitually alter their formulation and I suspect 77 in this case too. The only blue in the whole of Humbrol and Revell range that did not have a green element is 14 and that worked with 32 but the white needed reducing with some black. Satin overcoat is recommended on a model since using H85 s/g will render the resulting colour too glossy. Finding a lighter colour on various parts of actual vehicles is no surprise since they needed a comparative undercoat before assembly and final painting.

Another point that I discovered is that the RAF did not start carrying the right front roundel until May 1941, probably because even by then as some vehicles were using army type camouflage colours, civil amd military police could not distinguish between them. Before May 1941 RAF vehicles carried a paper sticker in the front lower left corner of the windscreen with the letters 'RAF' thereon. Whether white on black or the reverse as yet I do not know, perhaps either would do.

Thanks for your very helpful reply.
I never realised that manufacturers of paint reformulated their products every now again, rendering carefully researched mixes no longer correct. Sneaky, what?
The bit about the RAF roundel is fascinating and could potentially be quite helpful in dating some images as being pre or post May '41 (in Britain, I must presume that getting the updated look took longer in the Middle and Far East). I'd just assumed that those vehicles lacking the roundel were not properly painted or just rarely left their airfields and so didn't need a roundel!
Thanks once more for your efforts on our behalf; not knowing what is right is the easy way out, but actually having the knowledge there means you should at least try to do it correctly.
John

Not 100% reliable as it is possible that some RAF units may have taken it upon themselves to apply such a marking on UK vehicles that moved from 'drome to 'drome before that date. In M.E. I have seen vehicles with 'RAF' in black on the cab door and no roundel or other marking either. RAF ME was something rather automomous and may have had their own regulations as did the army when it came to colours and markings. So far I only have the UK AMOs.