I make it turn face up twice pattering with something like "Whew! Glad that worked. Let me see if I can't get it again." The second time I do it a bit slower than the first, but still quick enough they don't see the "move."
And then I ramble something along the lines of "I've never done it three times in a row before. Let's see if I can't set a new personal best."
And then when it changes color, "Yup...I was afraid of that."
It really is an awesome trick.
David Acer has a similar effect, and it is debatable that it's more visible, on his DVD "Extreme Close-Up."
You can watch it here:
http://www.youtube.com/watch?v=MiMEfKUErfQ
The effect above starts at about 1:25.
Acer is amazing though, he has great material.