Cool vs Warm
The distinction between warm and cool colors has been important since at least the late 18th century. The contrast, as traced by etymologies in the Oxford English Dictionary, seems related to the observed contrast in landscape light, between the "warm" colors associated with daylight or sunset and the "cool" colors associated with a gray or overcast day.
Warm colors are often said to be hues from red through yellow, browns and tans included;
Cool colors are often said to be the hues from blue green through blue violet, most grays included.
The determination of whether a color appears warm or cool is relative. Any color can be made to appear warm or cool by its context with other colors.
Warm colors are often said to be hues from red through yellow, browns and tans included;
Cool colors are often said to be the hues from blue green through blue violet, most grays included.
The determination of whether a color appears warm or cool is relative. Any color can be made to appear warm or cool by its context with other colors.
warm/cool contrast effects

warm vs. cool colors in the color circle
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.
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.