e, complementary color effects that involve green vs. purple should be qualitatively different from the contrasts around warm vs. cool colors.
unsaturated color zones
A major feature of the warm/cool color contrast is that certain kinds of lightness or chroma contrast cause perceptually unique colors to appear among reds and yellows but not among blues, greens or purples. These new colors are brown, ochre and green gold.
They cannot be produced by manipulating the brightness or colorfulness of an isolated red, orange or yellow color area; they only appear in the contrast between related colors. Yet they appear perceptually very different from the saturated hues: brown looks nothing like orange, and green gold nothing like yellow.
I've called these unsaturated color zones. (There doesn't seem to be a standard name for them; some texts refer to them as "grays".) The chart below suggests the color variety they produce, in comparison to two shades of green.
unsaturated color zones
warm colors at optimal lightness (L) and chroma (C, middle row), with reductions in lightness (top three rows) or in chroma (bottom three rows) to 80%, 65% or 50% of the optimal values; focal locations of green gold, ochre and brown are outlined
In fact, as shown above, these colors can be produced by reducing either the lightness or chroma of the pure hue, although lightness has a greater impact than chroma across all hues, and lightness contrast is most important and chroma contrast least important in light yellow hues.
Boundary of Unsaturated Color Zones. The unsaturated color zones only appear within a limited span of the color wheel, roughly centered on the warm end of the warm/cool contrast at a CIECAM hue angle of about 35°. This splits the color wheel into two parts: the relatively small area between red and yellow where the unsaturated color zones appear, and the much larger circuit of violets, blues and greens where they do not.
The diagram shows the approximate extent of these browns, ochres and green golds as a proportion of the lightness of "pure" (most saturated) colors in a typical artists' color wheel, which puts the pure pigments at the circumference. Color markers are indicated by pigment color index name. The boundary of the unsaturated color zones defines an involute starting at the neutral tone for a magenta, increasing rapidly in relative lightness through the reds and red oranges, and finally intersecting the most saturated yellow green color at a hue angle of around 110°. The approximate location of focal brown, ochre and green gold are shown for reference.
unsaturated color zones in a generic color wheel
boundary of unsaturated colors as a proportion of the lightness of pure pigment color, at hues anchored by common pigments
The boundary is difficult to summarize in terms of chroma or saturation changes. The gist is that:
Mixing the pure color with white never produces these new colors; it only produces a pastel or tint of the color and typically shifts the hue as well (toward yellow for oranges or deep yellows, toward violet for reds and bluish reds).
Mixing the pure color with black ("lightness boundary", above) always produces these new colors, as it reduces both lightness and chroma; the impact of added black is strongest in light yellows (where a 5% reduction in lightness will shift the pure color into green) and weakest in bluish reds.
Mixing the pure color with a gray of equal lightness ("chroma boundary", above) typically produces these new colors, as it reduces chroma only; the effect is strongest in hues from yellow to scarlet. Added gray does not produce a categorical change among light yellows, as these already have a lightness close to white.
An interior boundary between the unsaturated colors with a reddish or greenish appearance crosses underneath all yellows and turns toward the achromatic center of the color wheel at around a hue angle of 60°, approximately the location of isoindolinone yellow (PY110) or nickel dioxine yellow (PY153). Colors near this green boundary have a greenish appearance (for example, 