I'd thought if it's a legal food colouring, it must be safe.

我觉得如果它是合法的食物染色剂的话，应该是安全的。

I still insist that the girls learn how to make food colouring in the old traditional way.

我仍然坚持让我的女仆们学习如何用古老的传统方法制作食用色素。

But once we add some contaminant to it, like food colouring for example, we say it's impure.

可是一旦我们在其中添加一些污染物，比如食用色素，我们就会说它不纯净。

While the cucumber is still warm, pound it to soften it a little and then add a little green food colouring.

趁黄瓜还热乎着，拍软捣碎，之后加入绿色食用色素。

Colour the icing with a little green food colouring.

【colour】用一点点绿色食物色素给糖霜着色。