AFAIK all railway issue Bardic lamps have the yellow filter fitted, it is simpler and cheaper to make only one version of the colour filter assembly.
For some railway jobs it was considered that a lamp showing only red/green/white was preferable.
This was achieved either by fitting a knob so designed that it would not turn to the yellow position, or by fitting a segmented brass washer inside the lamp that prevented the operating shaft being turned to the yellow position.
It is a simple matter to modify the lamp to show yellow if desired.
There was also a lamp made with red/green/white/BLUE aspects these were intended for police or military applications, not railway use. They are very rare.
Bardic industries also made a white only, non signalling rechargeable lamp, these were very much brighter than the signaling lamps powered by disposable batteries. (they make excellent detachable headlights for steam road vehicles)
These are not readily available anymore.
Bardic lamps were made in various case colours, the usuall convention being
National rail network-----------------------------silver or natural aluminium
Military issue------------------------------------Olive drab
Sold to the public via electrical wholesalers-------Yellow
Rechargeable, non signalling----------------------red
Flameproof version-------------------------------blue.
I have seen black ones, but suspect that these are home painted, not supplied like that.
Black looks better used for headlights or tail lights on vintage steam road vehicles.