Isn't that just 50s all-over crimson? crimson & cream without the cream.
My interpretation of Parkin, which mainly deals with Mark 1 stock, is that from 1949 to 1956 just about everything on all regions was painted in the original BR crimson lake. This would include stock on the Southern Region: anything to be seen in green was in the old Southern Railway colours, possibly revarnished or touched up.
Thanks for the info.
It certainly looks very striking in the few colour photos from that time.