So I think what Christopher is talking about is that there are two definitions of “cold reading” in play here:
1. Technique: This is an actual technique that investigators use to determine if someone is lying or telling the truth. You pick up in visual queues such as pupil dilation, fidgeting, speech patterns, etc. This will take years to perfect and is not really practical to use in a performance piece unless you plan to do an actual cold reading demo.
2. Performance: 99.9% of the time if am magician or mentalist says they are cold reading, they are not really using the technique. They are more than likely pretending to use cold reading as part of their performance."
These are good points, but I have a recommendation for how you can combine elements of both the investigation aspect and the performance aspect, particularly since you mentioned that your goal is to use cold reading (well, at least a facsimile of cold reading) as a means of "deducing what card the spectator is thinking."
That's It, by Eddie Fechter can be a highly entertaining and fun card trick that directly involves the spectators. In case you are not familiar with it, the basic plot is that a card is selected and "lost" in the deck. The magician shows the spectators cards, one at a time. Each time they are shown a card, they are to say "That's it," regardless of whether or not the card truly is the selection. They can be told not to change the tone of their voice, their facial expression, or their body language when they are shown a card and say "Thats it." But you tell then that try as they might to hide when they are not telling the truth, you will be able to deduce what their card was by the look in their eyes, the tone of their voice and their overall body language. And that's just what you are able to do, even though they believe you have failed, and as a bonus, there is a very surprising and magical revelation of the correct card at the end.