I saw this drawing a while ago and LOVE it! Today I found a website about the different costumes for POTO and found more info about the Wishing Dress. I bet you probably already know this stuff about the dress/fabric but I thought that I'd post it just in case you didn't.
[link] ---4th paragraph down: "The blue silk for the costume is said to be woven in India and specially printed in England for the POTO production. Let me tell you a secret... it's not! The exact same fabric has been used in "Dangerous Liaisons" (golden version) and "Forsyth Saga" (blue version). So it IS possible to get a hold on it, but I can guarantee that it won't be the cheapest investment you might do in your lifetime.... With a very few exceptions, the fabric is the same in all productions of Phantom around the world, and it takes around 18 metres of the blue silk. Antique braids, laids and buttons are also often used in the costume. The backside has waterfall backdrapes, alternating between the blue silk and darker blue lining. Underneath, the dress has a small bustle (often of a padded fabric) which is attached to an underskirt. The original underskirt was white, but nowadays most are made of navy silk/satin. The bodice and skirt is separate, but some are attached together with hooks and eyes. "---