Why can magenta-cyan color separation film be obtained by adding red, green and blue filters in color separation photography?

The filter you added is a panchromatic filter, also known as a black-and-white special filter. It is used for black and white photography. After adding a panchromatic filter, some colors of visible light will be filtered out, so the colors will become unbalanced and the negative will show other colors. I suggest you go to Mai Sha to find out about photographic equipment. The column of photography technology introduces the characteristics and usage of various filters. I've seen it there. For the red, orange, yellow, green, blue and blue colors of a full-color filter,