Apply filter(s) that are a minus type. When you filter for B/W you are not adding colour but subtracting (neutralizing/removing to whatever degree) the colour. A minus yellow (blue), minus magenta (green) or Minus red filter (cyan) or the combination of these would tend to get you close to ortho on a pan film.
And my example showed a demonstration of that effect as well as the pigment material. This demo has been used world wide to demonstrate all of the elements of filtration, color and the differences between the different methods of filtration and color reproduction.
I'm sorry if it seems to have offended one member here. As I said, look at the demo and make up your own mind.