Not really a story or world building. Just some character design.
Cadance likes to hide her wings with both a spell and a poncho. It lets her go unnoticed into towns and meet people.
Blue is a rare color for fabrics but’s just a small amount for her ribbons so few notice. As for how she got those rare fabric, Cadance has some connections to some very old ponies with a trove of treasures amassed over a very long time.