I wasn’t aware that BR specified cab interior colours as it wasn’t a ‘public’ area. The various works continued with the schemes of the previous companies, eg. Ex LNER & GWR - body colour, ex LMS - black below waist & white above (as the L& Y loco above) & ex SR - black below waist and light stone above.
I would love to see some evidence that I’m wrong, but I’ve not seen any yet. Another thing that bugs me about cab interiors on models (and preserved locos) is the painting of control handles and wheels red. It never happened, they were either unpainted brass, bronze, iron, steel or wood or, if painted, they just matched the rest of the cab (again see above photo). One exception is that at some point in the twenties or thirties the GWR specified Venetian Red for regulator levers. Venetian Red is red oxide.
Ian R