On what basis are colours divided into warm and cool groups?

Correct answer: Perception of visual temperature

The governing concept is colour temperature, which is a perceptual and expressive classification rather than a measurement of actual physical heat. Colours are called warm or cool according to the visual and emotional sensation they create: reds, oranges and yellows often suggest warmth, while blues and blue-greens suggest coolness. The price of paint, paper type and brush size may affect materials or technique, but none determines this classification.