I have an idea for a routine where I would present a packet of Blue bikes, open it up and take off the top four cards (which happen to be the four Kings). I would then go straight into David Regal's 'Off With His Head' (a favourite packet trick of mine).
Then the full deck comes into play, and (still without the four kings), I would ask the spec to choose a card and turn it face up. I open up a Red deck and - magically - their selection is face down in the red deck! The kings are also not present in the red deck.
To close, I wondered about using Aaron Fisher's 'Panic!' (blue back) to shut the routine down and re-reveal the Four Kings.
Any thoughts would be great.