Did you know that butterflies can see a greater range of colours than humans?
Apparently they see ultraviolet light as well as what we call "the visible spectrum".
This must make things very difficult for your average Red Admiral who enjoys a bit of railway modelling when not supping from the blooms. How much harder it must be to work out which pot of colour you require from the Humbrol rack. Worse, they don't even produce any ultraviolet tins so you'll have to mix your own.
All this came to mind because I've been trying to match the body colour of my Y6 tram loco to the models I have found. Since there don't appear to be any colour snaps from LNER days available to me, I'll have to rely on other peoples interpretations.
My feeling is that the brown is quite light so I plumped for No. 62 - Matt Leather. Having sprayed it over grey primer, it might be on the light side but once a few coats of mucky brown weathering are in place, I bet it looks OK. The paint probably faded a bit when exposed to sunlight anyway.