To Subtract all light we would use all three filters.
To subtract red light you use a green - blue (cyan) filter.
To subtract green light we would use a bluish - red (magenta) filter.
So yellow, magenta, and cyan are anti or complementary colours to blue , green and red respectively. This inter - relationship is VITAL for the understanding of colour processing and printing.
These principals are used in both the composition of colour film and making enlargements in colour.