The colour wheel can be divided in two halves based on the effects of the colours in each half on the viewer’s feeling of warmth and coldness. The warm half ranges from yellow to red-purple; the cold half ranges from yellow-green to purple. The contrast between cold and warm colours relates first and foremost to our overall feeling about the coldness or warmth of an image, but on a second level also to effects on the viewer’s feeling of depth. When placed in front of warm colours, cold colours seem to merge into the background of an image, while the other way round, warm colours in front of a cool-coloured background seem to move into the foreground. The strongest depth effect of this type is achieved between the complementaries red-orange and blue-green.
