ll shift toward purple, rather than gray, when mixed with a blue paint.
In most representational works, the coolest hue is the visual complement to the color of the illumination. As landscape light declines toward sunset, for example, the color of the sky becomes more greenish, appearing cerulean just before sunset.
For representational modeling, the most versatile shadow colors are iron blue (PB27) and indanthrone blue (PB60). Both are remarkably versatile and effective shadow colors; iron blue is appropriate for shadow tints under "red" or late afternoon light or weak incandescent lamps, while indanthrone blue is best for shadows under intense incandescent or natural daylight. For more expressive or coloristic effects, almost any paint from perylene maroon to phthalocyanine green can be effective.
How do I mix any specific color to make it warmer or cooler? Again, this depends on whether you want to model the effects of natural light or create an abstract color design, and which specific color you intend to shift.
All warm hues are made warmer if they are darkened, dulled or mixed with any paint that does not contain "green" or "blue" reflectance, which can raise the S cone response. Oranges or yellows make a brown color similar to burnt sienna or yellow ochre if mixed with purple, which warms them, but these mixtures characteristically shift toward red rather than yellow when lightened. The saturated "blue" reds (which include all quinacridones and many naphthols, perylenes and pyrroles) shift toward blue when diluted or mixed with white paint, sometimes by as much as 20° hue angle.
Warm hues are made cooler if they are neutralized by any green or blue paint, which shifts them toward gray without proportionately darkening the color.
Blues are warmed by mixture with any magenta, red or orange paint, up to the point where they become purple. Blues are generally cooled by mixture with yellow, but greens are warmed by it. Greens are cooled by mixture with purples or blues.
How do I decide if a color is relatively warmer or cooler than another? There are three possible definitions of "warmer": (1) contains more yellow; (2) contains more scarlet (red); (3) is closer to gray.
If you want to convey luminance, then yellow mixtures and yellow bias in reflectance curves is the key; you need to know how to increase or decrease those in any color by paint mixtures and how to harmonize the yellow content of paints in a total painting.
if you want to convey dryness, lack of moisture, heat, intensity, then the same is true, only now your focus is on red (any scarlet or red with no blue reflectance cadmium red deep is ok, quinacridone red is not).
N E X T : color wheels
involute of "warm" hues in CIECAM