The knowldible folks who discuss Adeniums on the Yahoo group say that double parents make about 10% double babies. And one lady there has a seedling from plants she pollinated that she says is quite fragrant.
Stranger things have happened! Choochart, the fellow who owns Siam Adeniums was hoping for a blue, before the floods, anyway. I believe he had contracts with a lot of growers, but I don't know that for sure.