I'd appreciate some advice on an idea I have.

Here's how it should look, and what the audience should expect:

A young lady rides a beautiful Arabian horse on stage and stops center stage. She turns and waves to the audience. There's a flash of light, a puff of smoke (or whatever), and . . .

(The audience should expect that the horse and rider will have vanished, but . . .)

there's the young lady, still waving at the audience. But the horse, which was bay (medium brown with dark brown mane and tail) is now white! She rides the horse off-stage.

I have an Arab mare, bay, and an Arab gelding, gray (practically white), and they're the same height and physically very similar except for the color. I'll need to get twin girls who can ride, but that shouldn't be too difficult. What I lack is a good method. I have an idea, but it'll take some work.

Any suggestions? Thanks!

If I were to do this effect I would play around with peppers ghost illusion. Depending on the exploasions and there timing this could be very effective.

I was going to say something just like that Gracy... amazing what a good mind reader you can be at times

It the whole last name thing

Precisely what I was thinking. The cabinet & glass will have to be huge, and it will be pretty angly, but if I could make it work I think it'll play amazingly well. As I said, the big advantage is that the ending will be completely unexpected.

Any carpenters out there? Do you do windows?

Nope

But you will get it built as long as you work hard and try.

The Blue Room, or Pepper's Ghost does seem a bit impractical and expensive, have you thought of using black art and scrim? If you're playing a roadshow this might be a better solution. Lee Grable's book details the Thurston, the Blackstone and two of Grables time tested methods which might be adapted to your purpose. If you're touring, some compromise might be necessary.

I'm unfamiliar with scrim. Have you a suggestion where I might locate Mr. Grable's book? Thanks!

I bought mine at the recent IBM Convention. It should be available at Magic Dealers. Try Hollywood Magic. Also try Lee Jacobs in Pomroy Ohio. There are a lot of magic book dealers available through the internet. Scrim is a theatrical drop which becomes transparent when lights are lowered on the front and brought up on objects behind it. It is available through theatrical supply houses like Rose Co. in L.A. It is used for transformation effects. If all you want to do is change the color of a horse on stage, there are a number of optic possibilities.