Simple past tense and past participle of discolour.(verb)
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Use "discoloured" in a sentence
"It is, however, a very bad plan, as air and light are particularly necessary to seedling plants; and when they are even partially deprived of these important agents, they become drawn up with weak slender stems, and thin discoloured leaves."
"With pasta or potatoes, the water is often starchy and with veg such as broccoli, the water can be "discoloured" from the veg itself - so not really suitable for washing stuff."
"The nails were discoloured and black, while the skin was already grained with dirt which even a scrubbing-brush could not remove."