I am planning to make some gauge 3 models of the Brill Tramway. There is a fair amount of information on the stock, where it came from and how it was used, but all the information is pre 1936, and hence pre colour photography. I guess the line did not have pretensions towards a "Livery" as such, and the later coaches were probably to the same teak finish as the rest of Met compartment stock. But what of the earlier stock? The 2-compartment composite coach, the Bristol built tramcar and the Manning Wardle K class locos? The only one I know of is the chain-driven traction engine in the LT museum.
This enquiry reminded me of an amazingly comprehensive book of fifty years back which might be of some help. It was printed in black on white back then, but with a colour chip card enclosed to make clear the various shades of different railways over the years. Google suggests it was “Britain's Railway Liveries - Colours Crests and Linings 1825 – 1948” by Carter, Ernest F, published by Burke in 1952, and Harold Starke in 1963 and 1979, with fold-out colour chart, colour plates, b&w illustrations, xvi + 350pp.