The pipes were beginning to rust, discolouring the water.

管子开始生锈，水都变颜色了。

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。

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.

投手则被禁止发人为旋转或轨线的球，例如给球切口或在球上戳刺，也禁止投手用污垢、烟草汁、头油让球变色。