It isn't often we get the opportunity to peer inside a billionaire's wardrobe, so when Mark Zuckerberg posted a photograph of his online this week, the world scrutinised minutely. Would there be bespoke, fat cat-style pinstripe suits, we wondered? A row of Rolex watches? Shoes with goldfish contained in the heels?No, none of those.The Facebook co-founder revealed a wardrobe via an update - on Facebook, obviously - in which he joked about facing a tricky sartorial choice upon his first day back in the office after paternity leave.Rather than any ostentatious designer workwear, Zuckerberg's wardrobe featured just a row of grey T-shirts and grey zip-up hoodies. The morning routine of an entrepreneurial genius, it seems, is to save the unnecessary time spent deciding how to change outfits each day.To keen observers of Silicon Valley fashion trends, Zuckerberg's choice of T-shirts and hoodies is no revelation.The 31-year-old has rarely been seen in anything else, it being the unofficial uniform of tech start-ups. Removing all semblance of colour variation, however, is a bold new step.Commentators were quick to comment about the billionaire's post. Taking an almost financial hack angle, Lou DiMaggio suggested Zuckerberg's saving on different coloured T-shirts could be a reason for his enormous personal wealth.He wrote: ''When your entire wardrobe consists of a sweatshirt, you can afford to live on a billion dollars." ..