So how to explain the new trend for blue nail polish? Blue. On fingers. Blue, the colour of extreme cold. Of sickness. Of depression. The colour that if our dinner companion turned we'd start desperately hoping we could properly remember the rules of the Heimlich manoeuvre. Blue!

I am, I admit, a traditionalist when it comes to varnish: nude or red of all shades are pretty much where my manicure universe begins and ends. But at London Fashion Week last week, I started to admit that I might be wrong. Many girls - admittedly younger than me - were sporting blue nail varnish. And it looked good. Very good.

It didn't make me think of consumption; it made me think wistfully of the shades of a night sky before all turns dark, of that light at dusk when things still hold magical possibility, when promises can still be made - or not yet broken, when shadows are a good thing.

Besides, it turns out that this stuff is flying off the shelves. When O.P.I. launched its "Russian Navy" shade of varnish in November, one Manhattan boutique sold 1,800 pots of it in 24 hours and since it launched in the UK it has sold out three times. Plus its new "Yoga-ta Get this Blue" shade - more indigo-ish for spring ( pictured, right ) - is already trotting out of the door.

So I decided to give it a go. It turns out it I even like it on me - it's just a question of getting the right shade for your skin tone. For me, with blonde hair and a slight orange tone to the skin, that's Chanel's Blue Satin. It's the same take on blue as its Rouge Noir is on red: it's a deep, velvety, hard-to- pin-down mix of blue/black, a will o' the wisp of colour. And it's easy to team with almost any coloured clothing.

Then there's Essie's Aruba blue with its lighter, brighter, kind of Renaissance tone; Botticelli would probably have loved it. And most women will too - although I suspect this shade lends itself better to younger hands. But I could be wrong. Or even being ageist. Perhaps blue varnish will become the denim of the beauty world - the ultimate liberator.