No-fuss Princess Anne always manages to look effortlessly elegant, and she could teach the trend-obsessed out there a thing or two about reaching into your own closet. The Princess Royal beat the stifling U.K. heat in a butter yellow gown while attending a dinner for the centenary celebration of the Honourable Company of Master Mariners—and her floral dress still fit perfectly, despite being nearly as old as her middle-aged children.Princess Ann…