From Longman Dictionary of Contemporary Englishdiscolourdis‧col‧our British English, discolor American English /dɪsˈkʌlə $ -ər/ verb [intransitive, transitive] CCMARKto change colour, or to make something change colour, so that it looks unattractive Once cut, apples quickly discolour.→ See Verb table
Examples from the Corpus
discolour• Reject any that are even slightly soft or in any way discoloured.• Stainless steel cutlery Can discolour and pit if left coated with food, so use the pre-wash cycle.• They were housed in a type of guttering that had discoloured and so much of the light was lost.• Over the years this must have harmed his chest, as it had already badly discoloured his teeth.• Leaking, discoloured, swollen, rusty or corroded batteries should never be used.• Blood from his head discoloured the blue tiling pattern of the plastic liner around him.• In ditches and damp springs, you may sometimes notice that the water is discoloured to a strong shade of orange.• When buying, avoid cheese that is discoloured under the rind. 