“Colours can be classified as warm or cool. Warm colours such as red, orange, or yellow, tend to be exciting, emphatic, and affirmative. In addition to these psychological effects, optically they seem to advance and expand.”
“Cool colours- blue, green, or violet- are psychologically calming, soothing, or depressive, and unephatic; optically, they appear to recede and contract. These characteristics are relative, however, since intensity and value also affect the spatial action of warm and cool colours. Intensely coloured shapes appear larger than duller ones of the same size. Light-valued shapes seem to advance and expand while dark-valued ones seem to recede and contract.”
To get a better feel for this, go and look at some on-line art and examine the works with warm and cool colours in mind.
For the classroom, warm and cool colours can be the focus of any art lesson.
Quotes from: Drawing: A Contemporary Approach, Third Edition, by Claudia Betti and Teel Sale, Pub. Harcourt Brace Jovanovich, 1992.
My Many Colored Days by Dr. Seuss