I’d not heard this phrase before talking to my friend Sarah about idioms (whose wonderful mum apparently says things like this all the time). It can also be used to refer to oneself, ie “I’m not as green as I am cabbage looking, y’know.”

It means to not be as stupid or naive as you might appear. I can’t find out much about the phrase’s origins – I need more books on dialect – but it seems to be used in Lancashire, Yorkshire and maybe Ireland. It’s another one using a common vegetable, which I would say suggests it’s a phrase from working people.

This idiom also shows how much we use colour in language as shorthand for other things. As a metaphor for immaturity and inexperience, green is the natural choice for most of us. It makes sense, somehow, and it’s so embedded in our culture that associating those qualities with a different colour would just be wrong; which is one reason why BBC Horizon the other week was so fascinating.

Exploring whether colour was experienced in the same way by everyone, the programme found that how we describe colour has a key role in how we see it. It also featured a woman who could see, but only in black and white – the world was various shades of grey for her. Nevertheless, although she has no concept of actual colours, she understands cultural associations with colour words, such as ‘blue’ for feeling sad.

But really it’s just a word to her. A linguistic construct. The thought of which (imagine a world with no colour!) certainly makes me feel blue.

Next week’s idiom: Swings and roundabouts.