I am not even suggestion doing an actual cold deck. But for demonstration purposes doing any color changing deck and calling it a cold deck will work. Follow it up with and obviously stacked hand and I think it will play great. I definitely think some sort of shell game or three card monte would be great....I just wouldn't do both.
If you're going to demo something for an audience and if you have to choose between the shell game and three card monte... I say three card monte.
But yeah, using both kills it, because for the second one, they'll obviously already have an idea what's going to happen in the end.