Warm/Cool -Warm/Cool colors or color temperature refers to the physical or visual heat suggested by a color. Warm colors such as yellow and red make reference to warm objects such as fire and daylight while cool colors such as blue and violet refer to cool objects such as ice and overcast skies. In the visible spectrum, warm colors have higher wavelengths than cool colors. As a result, warm colors are said to 'visually advance' while cool colors 'visually recede. This is due to the wavelengths of the color - higher wavelengths are more difficult for the eye to translate and thus the eye tends to focus on the higher wavelength colors.
Color temperature is measured in Kelvin -- a candle flame is approximately 1850K, daylight is approximately 5000K, and afternoon daylight is approximately 6500K.