darken and the "red" component to appear unnaturally bright. This causes greens to shift toward yellow and the dull yellow or red of tree bark and wood to appear unnaturally red.
Night light is is viewed under scotopic vision, which means colors are principally symbolic rather than imitative. Even so, the typical representation of night relies on a near monochrome palette of blues or blue greens, with yellow accents contributed by isolated artificial lights and the near surfaces they illuminate.
How do I make a color warmer or cooler? The answer depends on whether your axis of reference is the illumination or the hue circle. If you want to make a color warmer within a certain kind of illumination (that is, the light in any representational landscape or portrait), then the "warmest" color is typically shifted from red orange toward the color of the illumination. Greenish light makes oranges and yellow warmest, because reds are dulled almost to blacks; orange light makes oranges warmest, and dulls magentas and yellow greens.
If the axis of reference is in terms of the hue circle (as would be used in nonrepresentational color design, for example), then "warmest" color depends on all the colors in the image. However, given the way our visual system is structured and the range of available pigments, a red orange located at a CIELAB hue angle of about 40 or darkened, whitened or dull paints of similar hue, such as burnt sienna, burnt umber, convenience "naples yellow" paints, or quinacridone orange are good standards of comparison.
When you "cool" a warm color in paint mixtures, it is important to use a blue that contains no red reflectance and no green hue. In paints, only indanthrone blue (PB60), phthao blue (PB15 or iron blue (PB27) meet these two criteria. All paints compounded with ultramarine blue or cobalt blue contain some "red" reflectance and give the mixture a purple tint. At the same time, paradoxical shifts can result if you use a saturated "blue" red that contains some "violet" reflectance. This paints will 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 