cocosa.comtrend tracking24- The Devil Wears Prada -How and why do different designers know to back specific trends for a season? Lauretta Roberts, creative director of trends website WGSN Boutique, explainsThe famous 'cerulean blue' monologue in The Devil Wears Prada nicely sums up the trickle-down trend effect from catwalk to high street shelf - but is it that simple?The British high street has become so adept at distilling catwalk trends for a mass-market audience, you could be forgiven for thinking that the big four - New York, London, Milan and Paris - are solely responsible for setting the high street's trends. Of course they have a significant influence, but inspiration also comes from further afield.When it comes to backing a trend, commercial aspects also come into play. What's been successful before is often refreshed by retailers to sustain its profitability. Autumn's Navajo morphs into spring's tribal trend, for instance; or there is a marked about-face to deliberately render the previous season's look outmoded in an effort to encourage consumers to spend again.Obviously there are always some retailers and designers who march to the beat of their own drum. Miuccia Prada and Christopher Kane are examples of designers whose originality often evades the metrics of prediction. For an example of where fashion trends come from, we need to rewind two years to when WGSN's trend scouts were stalking the streets, attending global fabric fairs, colour seminars, and assessing broader movements in culture, economics and society - all in a bid to identify three key SS12 macro trends that would direct the SS12 season.Here's how they translated.PREDICTING the trends"You select that lumpy blue sweater. But what you don't know is that sweater is not just blue...it's actually cerulean. In 2002, Oscar de la Renta did a collection of cerulean gowns...and then cerulean showed up in the collections of eight different designers..."