(From Disney Shawn's blog)...new details and "secrets" added since the renovation was complete.

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Look at the inlaid star pattern in the floor at the threshold of the shop...Castle Couture is the Royal Dressmaker for the Kingdom of Fantasyland, and the story shows that it's clearly run by the three good fairies from Sleeping Beauty. The stars represent them: Red for Flora, Green for Fauna, Blue for Merryweather.
The second half of the shop, once home to Tinker Bell's Fairy Treasures, has been converted into an expansion of Castle Couture.
The original section of Castle Couture is now the Dressmaker's showroom, ornately appointed and including facilities for young princesses to try on their new gowns. This new section represents the Dressmaker's Workshop. Here, the fixtures are made of wood and covered with fabric, thread and the tools of the dressmaker trade.
The walls of the workshop include nods to some of the Dressmaker's more famous clientele. Look for silhouettes of Belle, Ariel, Aurora and the fairest of them all, Snow White. You'll also discover art on the wall representing dress designs (in fact, these are reproductions of concept art for some of the Disney animated features).
The back corner of the workshop is dressed as a fitting room and portrait studio. Here, the gown being made at the moment is for none other than the queen of this kingdom, Cinderella. On an overhead shelf, you'll see her silhouette and a collection of blue fabric (her signature color).
Glance at the other side of the room, and you may notice a few other things among the notions on these shelves. There are pin cushions in the shape of pumpkins, and peeking out over the top ledge are Gus and Jaq, overseeing the work on the dress (and probably keeping an eye out for Lucifer).