Complementary colours
Complementary colours are pairs of colours that can be said to ‘complete’ each other. A complementary relationship can be established in different ways, two being widely accepted. By one definition, two paints, inks, or coloured lights are complementary if their mixture can yield an achromatic black, grey or white. By another definition, two colours are complementary if the afterimage of one colour has the same hue as that of the other. It is also common simply to claim that colours opposite to each other on a colour wheel/hue circle are complementary, without further explanation or justification, however as there are multiple ways to depict colour wheels, complementary sets are not unique.
The difficulty here is that the different ways of defining complementary relationships yield different pairings.
The most extreme case is with blue. To produce an achromatic or near-neutral dark grey by the subtractive mixing process, paint that appears blue must be mixed with paint that appears reddish-orange. To produce an achromatic white by the additive mixing process, a light that appears blue needs to be mixed with one that appears yellow. The afterimage of blue is a yellowish orange. So the complementary of blue can be red-orange, yellow, or yellow-orange, depending on how the complementary relationship is defined.
Example: Different ways to define complementary colours:
A) Via afterimage – the complement to blue is yellowish- orange. B) Via subtractively mixing paints to a neutral grey – the complement of blue is reddish- orange. C) Via additively mixing light sources – the complement to blue is yellow. Images courtesy of Paul Green-Armytage.
