As a user, the key thing I want from the livery is a quick sense check, possibly rushing onto a platform at the last minute, that the train standing there is likely to be the one I want. I can see it’s a train, so I don’t want branding to tell me that, but I do want differentiation between the fast one to London, the fast one to Birmingham/Exeter and beyond and the stopper to Severn Beach. Ideally inside as well as outside the train, and colour schemes matching those on route maps, such as LUL.
I still expect some form of express and slower service ticket validity differential to exist post GBR, which will be clearer to communicate with different colour trains rather than everything looking the same.
And if for resource efficiencies more stock does interwork, perhaps some clever temporary branding solution could be developed eg large coloured LED screens that change to reflect the service that unit is working.