ADDITIVE COMPLEMENTARIES

We've seen that each of the three colours yellow, magenta and cyan can be mixed from two of our additive primaries, and also that the three primaries make white light. It follows that yellow, magenta and cyan can each be thought of as being the complement of the one primary that is absent from the mixture, i.e. as needing the addition of that primary to make white. Magenta lacks green, cyan lacks red, and yellow lacks blue.

Figure 4.6: Additive complementary relationships.

The third of these relationships is the most surprising for painters, who know that if they mix yellow and deep blue (ultramarine) paints we will get green. Notice also that, contrary to both the conventional artist's colour wheel and the system of opponent colours of Hering, red is the additive complement of cyan, not green, and green is the additive complement of magenta, not red.

Since all of our possible screen colours can be mixed from the RGB primaries, we can sum up their additive mixing relationships on a triangular diagram, with the primaries at the corners and the relevant mixed colours in the middle of each side (Figure 4.7). This arrangement automatically places each pair of additive complementaries opposite each other.

Figure 4.7. Mixing relationships of RGB colours.

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