Tetradic palette generator

Gives four hues 90 degrees apart, which is two complementary pairs. It offers the most colours of any classical scheme and is the hardest to keep under control.

Four hues means four things competing, and unlike a triad the pairs also relate to each other, so a badly balanced tetrad reads as two separate palettes rather than one. The standard advice is to let one hue take most of the surface and use the other three sparingly, and to vary lightness heavily so the four are distinguishable by more than hue alone. If a tetrad is not working, dropping to a triad or a split-complementary scheme almost always improves it — the extra colour is rarely earning its place.