All depends on the maker, so as a rule of thumb . Most English guns colour hardened the action , forend iron , trigger plate, breech pin, tailpipe ,triggers,forend diamond and pin ,side plates if fitted , Deeley catches , snap box , cocking dog pins .
Cover plates ,push rods top levers and pins guards and pins were normally blacked /blued .
BUT some blacked forend irons and trigger plates this being dependent on the type of safe work and whether the gun was ejector , snap boxes. Safe buttons could be either as could many pins .
No pins were left white originally and trends have changed as to what and is not done in renovation , what is brushed an what is blacked . This I feel is down to the individual and the specific gun .