The pipes were beginning to rust, discolouring the water.
管子开始生锈，水都变颜色了。
《牛津词典》
2
Dice the apples and toss with a little lemon juice to prevent discolouring.
将苹果切片，和上少许柠檬汁防变色，沥干。
3
Pitchers were forbidden to give the ball an artificial spin or trajectory by, for instance, nicking it or spitting on it and from discolouring the ball with dirt or tobacco juice or hair grease.