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A colour cast is a tint of a particular colour, usually unwanted, that evenly affects a photographic image in whole or in part.[1]
Certain types of light can cause film and digital cameras to render a colour cast. Illuminating a subject with light sources of different colour temperatures will usually cause colour cast problems in the shadows. The human eye generally does not notice the unnatural colour, because our eyes and brains adjust and compensate for different types of light in ways that cameras cannot.
In film, colour casts can also be caused by problems in photo development. Improper timing or imbalanced chemical mixtures can cause unwanted casts.
Colour casts can also occur in old photographs due to fading of dyes, particularly under the action of ultraviolet light. These may be correctable on a scanned version of the photograph with image editing techniques.[2]