Lots of confusion:
“Black and white” not good terminology to use
Black and white photographs are not just black/white, but really greyscale
“Greyscale” refers to shades of grey, ie where the RGB values are all the same
“Monochrome” refers not to one colour, but historically to “one colour with black”, so “monochrome” really means two colours, usually black and white
“Monochromatic” in colour blindness refers to greyscale!