Thanks for the reply - veryy interesting.
My two swatches are as follows
Right - Tamiya XF-52 Flat Earth as given in their instructions for the Centaur
Left - Mix of Revell 84 and 86 (Ratio 16:5) as suggested by Mike Starmer on the MAFA.net site
In theory Mike Starmer's mixes should be spot on as he is his an expert in this field and research is very well regarded.
But I have never seen any vehicle presented in this chocolate brown colour either in document or museum exhibit.
I have seen vehicles in a caramel like colour similar to Tamiya XF-52 and your Vallejo colour at Bovington Tank Museum (a Convenantor as I recall) but when I spoke to the museum historian he was unable to confirm whether that was SCC 2 or even whether it was an accurate colour at all.
But I am loathed to say that Mike Starmers mix isn't accurate given the amount of research he has put into it. I may have made an error with the mix but both the Revell colours are darker than the Tamiya and Vallejo in their own right.
Incidently, where did you find the Vallejo mapping to real colours - I have been thinking of giving Vallejo a go because I have heard great reviews but I'm put off becuase I would have to mail order and unsure which of their colours would be suitable for my needs.
This is the Covenantor at Bovington

Mike Starmer's info can be found here
http://www.mafva.net/PDF/BritishCamouflage3.pdfSCC 2 is described as 'Rich Dark Brown with a hint of Khaki'
which I must admit, does not describe the Tamiya, Vallejo or Bovington Covenantor.
Cheers,
Nigel