ity.
The Univerity of Nebraska-Lincoln hosts a simple blackbody curve simulator that calculates the emittance spectrum and peak energy for a blackbody from 3000°K to 25,000°K. Mitchell Charity has posted several useful pages on blackbody colors with links to additional resources.
the warm/cool contrast in paints
I have explained why lightness and chroma are responsible for the "advancing" (spatial depth) or "arousing" (mood) effects attributed to warm colors, and why the warm/cool contrast is a visual adaptation to changes in natural light. The last piece of the puzzle is to explain how the warm/cool contrast appears through our perception of surface colors such as paints.
Unfortunately no modern color model represents the warm/cool contrast as a distinct dimension of color perception, so the answer has to expressed in terms of paint reflectance curves and their colormaking attributes.
spectral emission curve of a fluorescent "daylight" bulb with a CCT of 4370°K
from Wyszecki & Stiles (1982)
Green Is Neither Warm Nor Cool. If we compare the visible spectrum to the daylight color spectrum shown above, we immediately notice a glaring omission: there is no "green" in the daylight color spectrum.
The reason is that most noon daylight phases, with CCTs between 5800°K and 5000°K, are actually slightly green in hue (right, and above). Green is also the range of maximum reflectance in chlorophyll (which absorbs only short and long wavelength light) and therefore is the color of landscape vegetation. Green is not perceived as a sky color.
This green hue is briefly visible in the positive afterimage caused by glancing at the sun or staring at its reflection in a dark glass or water; but we are adapted to accept it as "white" light. (The afternoon sun appears yellow because atmospheric filtering has reduced its brightness and begun to shift the color toward red.)
As a result green is neither warm nor cool, because it is (at high luminance) associated with solar light and our perception of the white point or an equal balance between short and long wavelengths of light. So the warm/cool contrast is fundamentally a judgment of the balance in a light mixture between the wavelengths shorter than green (blue and violet) and longer than green (yellow and red).
Reflectance Criteria for "Warm" Colors. The next point is whether there are consistent attributes in the reflectance of surface colors perceived as warm or cool. There are, in particular for "warm" colors. These are apparent in the difference in color perception between lights and surfaces.
For all parts of the emitted spectrum that is, for colors of lights the relative saturation increases as the wavelengths of light are limited to a narrower band of color. At the extreme, a spike of single wavelength (monochromatic) light is the most saturated color stimulus physically possible for any hue at any brightness. And this is true no matter whether the hue is red, orange, yellow, green or blue.
Despite this, we find in artistic practice the consensus that only lights in the hue range from red through yellow to white are considered warm. A green or blue light, by itself or as the source of illumination in an architectural space, is not identified as warm and may even be termed cool. So although chroma or saturation may explain the arousing or advancing effect of warm colors, it does not by itself define an essential warm or cool color attribute. The same reasoning applies to the brightness or lightness of a color.
However, for reflected colors the colors of the real world the perception of chroma is more complex. As we saw in the discussion of optimal color stimuli, the maximum possible chroma for a surface color is defined by its lightness or total reflectivity, which means as colors become lighter they necessarily become duller. So the general rule for hue purity in surface colors should be: high saturation signals high reflectance within a limited part of the spectrum, although this means intense surfaces will also be relatively dark surfaces; pastel (light valued) colors typically ha