The colour wheel shows the relationship between primary, secondary and tertiary colours. In general, yellow is placed at the top of the colour wheel. From yellow, the colours proceed in a clockwise direction through the 'cool' colours on the right side of the wheel, to the 'warm' colours on the left side. Notice how the colours are grouped together: this is because they share certain characteristics. The 'warm' colours are red and yellow combinations - colours we associate with fire and sunshine - while the 'cool' colours are blues and greens - colours we associate with water, the sky and vegetation.
The 'warm' colours are 'advancing' colours: they seem to draw surfaces closer and create a cosy comfort. In interior design, advancing colours are often used to transform gloomy, north- or east-facing rooms. The 'cool' colours are receding colours: surfaces painted in them seem further away. Consequently, cool colours create a sense of space, making a room seem bigger than it actually is.