Treating Inky pHAT-Red as Black/White doesn't work

[TheMarrt]

Some resellers have this line in the product description:
"Pro-tip: you can treat the three-colour displays as black and white - InkyPHAT("black") - and they'll refresh as quickly as a black and white display, in just a couple of seconds"

I tried to overwrite/replace the auto detection in some scripts,
from inky import InkyPHAT
and then used
inky_display = InkyPHAT("black") instead of inky_display = auto(ask_user=True, verbose=True)

... the scripts run without error but the screen is not refreshed (but they will stop any ongoing 15s-Refreshes on execution, so there is something sent to the display)

What is the correct way to treat a 3-Color display as Black and White in the current version of Inky?