Dress robes are a formal variety of robes worn by witches and wizards for special occasions, and can vary in style and colour as much as everyday robes.
Harry Potter's first set of dress robes were cut in the same style as his school robes, but coloured green instead of black. By contrast, Ron Weasley's first dress robes were cut more like a dress and accessorised with a lace collar.
"Very simple white dress", accessorised with Muriel's goblin-made tiara of moonstones and diamonds
Behind the scenes
In the films, the design of wizards' dress robes is based primarily on tuxedos and fancy suits, as they are worn at similarly formal events. Dress shirts, waistcoats, and ties/bowties are all components of these outfits. Witches' dress robes are for all intents and purposes equivalent to Muggle dresses or gowns. These can be full length – falling to the ankles – or only extend as far as the knees.
The dress robes portrayed in the films tend to have a lot more added decoration, including beading, embroidery, frills, and intricate patterns in the fabric. The robes may also possess features that reflect something about the person wearing them:
Dumstrang students have short, fur-lined capes as part of their dress robes, reflecting the heavy furs normally worn as part of their school uniforms.
Parvati and Padma Patil wear robes inspired by the sari, a traditional Indian woman's dress.