It is a truth universally acknowledged that men rarely exhibit any interest in fashion. Seismic style shifts therefore are unknown in male dress with only the occasional tweak being registered. Very occasionally, however, something happens to men so that, like clothes-conscious lemmings, they all blindly rush to follow the same sartorial trend. The latest such movement has been in favour of blue shirts. There is no known explanation for this phenomenon. It cannot, for example, be ascribed to fashion designers since for years most of the better-known names have shown absolutely no interest in blue of any shade. You will not find shirts of this colour in John Rocha's current menswear collection, Gucci has not been an ardent promoter of blue for spring/summer 1999 nor is Giorgio Armani advocating its widespread adoption. Fashion designers do not produce blue shirts; they produce items like beaded sarongs which attention-seeking football players will want to wear.

Nor does the blue shirt even merit being classified as fashionable - primarily because it is not. Fashion at the moment favours the short-sleeved and tropical-printed. Think brilliantly-coloured parakeets flitting across your chest against a lurid sunset background: that's fashionable. Blue, no matter how intense the hue, simply fails to score in the high fashion stakes. Blue must settle for being merely popular. So here is a trend with entirely organic origins, produced without any visible prompting from the fashion industry. Men have taken the initiative themselves and chosen to adopt blue as their favourite colour for shirting, thereby jettisoning all previous popular choices such as white. In the 1980s (as a viewing of Oliver Stone's 1987 film Wall Street can confirm) striped shirts were the preferred choice for sharp dressers. Now they are worn by a handful of nostalgics. There has recently been a brief, but intense, flirtation with lilac but it cannot hope to supersede the colour of the decade: blue.

And not just any blue either but a very specific shade which might be described as deep periwinkle. This is blue with extra bite, categorised as French blue by shirtmakers Thomas Pink where it has been a steady bestseller since the company opened an outlet on Dublin's Dawson Street two years ago. Round on Grafton Street, blue is the most popular colour for shirting at F.X. Kelly - not just the aforementioned periwinkle but also, for more timorous souls, powder blue and what is called "Garda blue" too. Rich, bright blue shirts now stalk the streets with a blinding uniformity. Everywhere from banks to bars, the blueshirts are on the march, one member of the band hard to distinguish from the next. Their want of individual character is exacerbated by the shirt being invariably coupled with a gold or mustard-patterned tie; the only alternative in this area appears to be a red-based tie. Wearers - who tend to be in the 25-35 age group (or wish they still were) often share a number of other traits such as excessive dependence on hair grooming products, a fondness for thick-soled loafer shoes with metal bars across their front and a propensity to wear the same shirt at night and weekends untucked over jeans or chinos.

Appearing out of the blue, so to speak, will this trend ever lose its appeal? The answer is yes, because already the next fad for men's shirts is starting to make its presence felt. You read it here first: at the beginning of the next millennium, grey will be the new blue. Start stockpiling those shirts now.