That was brought up earlier. Almost all modern lenses are "achromatic", if not officially "apochromatic" (which in an official sense is more strictly defined for process lenses than general taking lenses). Some older lenses, prior to the 1960's were not always corrected with respect to the blue, so would benefit in black and white work from truncating the blue with a yellow, orange, or red filter. This was differentiated from "color" lenses, like the Commercial Ektars, which were expected to handle the full spectrum reasonably well. Nowadays we just take it for granted that
all lenses are fine for either color or black and white work. But older lenses still have certain qualities that some desire, or maybe you just got
ahold of one cheap.