This is from The Museum of Hoaxes
(
http://www.museumofhoaxes.com/ )
"So how is the trick done? Slate.com reports that:
the trick dates back to the 19th century, and the first English-language manual to describe the art was published in 1911. Back then, magicians connected the various layers via hook-and-eye fasteners; today, the literature describes no fewer than 15 different methods of pulling off the trick, using such devices as Velcro, magnets, and "fish bone pull fasteners."
In other words, it relies on special clothing and a lot of practice. If you watch the video closely, the moment when she has the hoop around her and changes from a green into a purple dress is the one time you can almost see the costume change occurring. I have no idea how she pulls off the trick at the end in which she changes clothes as glitter falls around her. "