Tetradic

Two complementary pairs give a picture more colour than any other scheme can hold without turning to noise. When it works it looks abundant rather than busy.

The difficulty is the point: it is the scheme that most obviously separates somebody who has thought about it from somebody who has not.

Choose two complementary pairs, so four hues in two oppositions. Orange with blue and green with red is the standard rectangle.

Rank them before you place anything. One pair leads and takes most of the picture. The second pair appears in small amounts only.

Balance the warm and cool totals across the frame rather than colour by colour. Four hues split evenly between warm and cool is what keeps it from tipping.

Use it for abundance: a festival, a market, a food event, a carnival, a textile, a pattern that has to reward a second look.

Leave it alone when the picture is small or fast. Four hues need room, and at thumbnail size they average into brown.

Triadic has three hues and no oppositions. Tetradic has four and two oppositions, which is roughly twice the noise and twice the reward.

A limited palette can also hold four colours, but it does not require them to be related. Here the four are two pairs.

Matisse's cut-outs run on it constantly, which is why they feel full rather than cluttered. So does most of Tropicalia, and so does almost every Persian carpet: two oppositions, ranked, with one of them quiet.

All four arrive at once and average into mud. Say one pair dominates and the second pair appears only as accents.

The frame tips warm or cool. Say the warm and cool totals are balanced across the whole picture, not within each shape.