(1) In fastness testing, any change in the colour of an object caused by light or contaminants in the atmosphere, e.g., burnt-gas fumes.
Note : The change in colour may be in hue, depth or brightness or any combination of these
(2) Colloquially, a reduction in the depth of colour of an object, irrespective of cause
Textile Resource (http://www.textile.org.uk)
