Idea
You right hand fan the deck to reveal it is blank. You take the spectators card and leave it out-jogged in the fan. Close the fan and move it to left hand grip. Now when you fan the cards, the deck has returned to normal and the selection has turned blank.
How can you change the card that is sticking out?
(all ideas developed by the community will be released at one point as a free release from the community)
I will need to experiment and get back to you then...
I would like for the color change to happen at the same time when you fan the deck to reveal it has returned back to normal.
I think it can be easily done if you are to transform the card blank and then fan the deck, but I'm not aiming for that hehe.
If the spectator isnt the one holding the double before its placed in the deck you could do a double and simply push in the selected card as you transfer the cards to the other hand and leave the sticking out card to be a blank card that was originally behind the selection. The only problem would then be the selection being seen in the fan. With some clever fan spread work that could be easily hidden though.