Charles,
Both totems were applied direct to the body colour paintwork. For the vast majority of the loco stock that paintwork was black. The usual alternative was BR's middle chrome green mainly used for express classes, although BR(WR) eventually began applying it to every loco they could. The 'cycling lion' was also found on class 8 express power when that bore the short lived blue livery very early in BR's existence, and the 'ferret and dartboard' on maroon painted BR(LMR) class 8 power. There were other exceptions, BR(ER) for example had some station pilot duty allocated small shunters turned out in pre-grouping liveries, but these were rarities.
As for nameplate background colour, BR standard was officially black from inception in 1948. Coloured backgrounds never completely went away judging by what photographic record is available, and subsequently crept back on many classes. Although red was the usual alternative, BoB pacifics had RAF blue. Personally I would go with the attitude that if you feel it enhances the loco, go for it.