It's probably been spotted already but you can get the technique of this in a short video at theory11.com.
It's in the 1-to-1 section (which you normally pay for) and it's absolutely free.
Jonathan Bayme presents it and makes it look so easy. Personally I'm still struggling just to do it and make it look difficult even!
Link is:
http://www.theory11.com/1on1/
Select Jonathan Bayme from the list on the right and it's "classic color change"