British Railways 1948 - 1965
The Big Four railways reacted quickly to the end of World War II by repainting their premier locomotives in their corporate colours and, although they were in a poor state due to the rigours of war, I believe that they would have gradually regained their pre war status. However, with a new Labour government and the scent of  "state ownership for everything" in the air their days were numbered. So, on 1 Jan 1948, British Railways (BR)was born.
During those first days the newly formed Railway Executive couldn't decide what the corporate colours for BR would be so, in the spirit of "let everyone decide" they experimented with various colour schemes. These ranged from a deep ultramarine blue to a lighter blue shade through lime green and ending up with a Brunswick Green. This latter colour was, to all effects and purposes, the GWR livery.