The Duchess of Cambridge's favourite styling trick is surprisingly simple: she routinely wears blue, her power colour. Over the years, she has experimented with crisp cobalt coats, navy suit sets, and other shades like periwinkle or indigo. Whether she's walking the red carpet or stepping out for a public appearance, it's a hue that makes her glow with confidence, and it's made us want to experiment with our own favourite tones.