If you add the three primary pigments together, yellow, red, and blue, you get black. If you add the three primary coloured lights together you get white light. The artist who works with pigment has to compromise, because he wants the effect of light but he cannot use light. For myself, in the field of relief printing where three or four opaque colours is the maximum number I can use, I would hold that the three basic colours must be present in whatever the combination of mixes, in equal quantities. It being more important that a third primary is not present in a mix so maximising the difference.
