When fashion houses from Chanel to J.Crew sent models down spring runways wearing pastel, lots of pastel, it was still possible to put off thinking about spring’s most prevalent trend: With months to go before clothing from the collections would actually be available in stores, shoppers at least had time to figure things out. Now here we are, a half a year later, faced with the challenge of trying to wear pretty new clothes in pale pink or light blue without looking like a giant preschooler. Or, as Back Bay wardrobe consultant Kerry Epstein puts it: “Most women don’t want to look like a baby duck.” Here’s how the experts say grown-ups can embrace the trend.