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Colour Fatigue can happen when we look at bright complimenting colours for extended periods of time, for instance, a wall mural made of YELLOW and ORANGE. We experience a vibrating effect; the colours start to dance around and pull away from each other. This happens as the retinas of our eyes have been exposed to a particular colour stimulus for too long and the optic nerve starts to send confused signals to the brain. Similarly, mixing complementary colours of the colour wheel (e.g.: PURPLE and YELLOW) should be used sparingly as it can grab attention but can tire easily.
Colour Washing takes place when our eyes are exposed to similar shades of a colour for some time. The colours seem to fade together and become the same shade. This is linked to Colour Fatigue as the optic nerve sends confused signals to the brain that the different shades are the same. This can be combated by using outlines between the colours, in neutral shades of WHITE, GREY or BLACK, which help the brain to separate the colours for better analysis. Such a method is used in glass-staining.