Colour Cast
An unwanted overall tint across an image, usually caused by the light source or by reflections from coloured surfaces.
In depth
A global cast from the illuminant is simple to remove with white balance. Local casts are harder: green light bouncing off grass onto a subject's chin, or warm light reflecting from a brick wall, affects only part of the frame and needs local correction. Recognising the difference between the two is most of the diagnosis.
Examples in practice
A portrait shot on a lawn shows green under the jaw that no global white balance change can remove without ruining the sky.