 The first member of the class was given a livery of plain black without lining ; this was changed to the new standard British Railways Brunswick green that was applied to express passenger locomotives after nationalisation , despite the locomotive being classed as mixed traffic . This was lined in orange and black , and the class was given the power classification 7MT . The " Britannias " were numbered under the new British Railways standard numbering system in the <unk> series . The locomotives were numbered between 70000 and 70054 , and featured brass nameplates with an initial black background , followed by red , located on the smoke deflectors . Towards the end of steam plain green livery was substituted , with the touching @-@ up of existing paintwork being preferred to full aesthetic overhaul . 
