son color or, closer to yellow or violet blue, if you prefer the alternative yellow/violet blue contrast. Thus, red is a warmer color than magenta, because red is closer to red orange; but both are warm colors in comparison to violet.
These relative comparisons are most often applied to analogous colors (of similar hue) a "warm blue" (compared to other blues) or a "cool red" (compared to other reds). Thus:
Occasionally a wider comparison is made across two or more hues, but it is still decided by the relative distance in a color wheel between the two colors and the warmest/coolest hue. Hooker's green is warm (closer to red orange or yellow) when compared with viridian, but is cool (closer to cyan or green blue) when compared with green gold.
It's always helpful to anchor the logic of this abstract color labeling in physical color mixing effects. Thus, the fact that hooker's green is warmer than viridian indicates that we can get a color equivalent to hooker's green by mixing viridian with an orange yellow or orange paint; the fact that it is cooler than green gold indicates that we can get hooker's green by mixing green gold with phthalo turquoise.
What about dull (near neutral) colors? If all colors must be either warm or cool, the common 19th century practice was to assign "gray" to the cool hues (as in a gray or overcast day). This is probably because most grays or dark neutral mixtures historically used in painting, including payne's gray, indigo and neutral tint, have been biased with a blue or green tint.
If colors are judged in relative terms, then a grayed color is either warm or cool using the same "distance in a color wheel" comparison as before. That is, a grayed blue green is warmer than a saturated blue green, because the gray is closer to red orange across the center of the hue circle. In paint mixing terms, some red orange has been mixed with the blue green in order to gray it, and this red orange appears as a warming of the color. (Again, it is always helpful to anchor the warm/cool labeling in color mixing effects.)
In general, all dull cool colors are warmer than their saturation hue match, and all dull warm colors are cooler than their saturated hue match. Thus, burnt sienna is cooler than cadmium scarlet, because it is less saturated (closer to gray).
The same principle applies if you are using the alternative yellow/blue violet contrast: ultramarine blue is made grayer (and warmer) by the addition of some burnt sienna, and burnt sienna is made cooler by adding some cobalt blue.
warm/cool contrast effects
Now we can address the third question raised above: what explains the visual or design effects created by warm or cool colors? In color theory writings the two most commonly described effects are:
warm colors "advance" in an image that is, they seem to stand out or attract attention, or seem spatially closer to the viewer, while cool colors "recede" or seem to melt into the background: they have a depth effect.
warm colors are active, arousing or cheerful, while cool colors are passive, restful or subdued: they have a mood effect.
Visual Associations. color theory typically explains these effects through absurd color associations "ice is blue, and so blue seems cool," or (my favorite), "a distant mountain appears blue, so blue seems to recede from us."
These fictions completely fail to explain the visual effects, because there are numerous and obvious counterexamples. For example, in landscapes the blue sky above us appears much closer than the whitish horizon, so why doesn't blue advance or white recede? If a sunset appears behind those blue mountains in the evening, why doesn't red appear to recede more than blue? On a hot summer's day a noon blue sky radiates far more heat than the reddish sunset, so why isn't blue warm and red cool? Why don't we say "snow is white, so white seems cold"? Or why is red warmer than white, if white hot is much hotter than red hot? It's astonishing that color theory writers have repeated these nursery rhymes, generation after generation, without any regard for the fac