Verb
change color, often in an undesired manner
Source: WordNetThe shirts discolored Source: Internet
Whatever the colour, turquoise should not be excessively soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolour over time and will not hold up to normal use in jewellery. Source: Internet
Prolonged exposure to direct sunlight may also discolour or dehydrate turquoise. Source: Internet