My favorite colour change is The Click Change, because the whole card is in view throughout the whole change. This, I think, makes the change that little bit more magical than ones with cover of some sort. It's also extremely instant and visual, which makes the reaction all the more extreme. However, as it is one of the most well known changes, if not the most well known change, to magicians as well as laymen, there is a chance that they have seen, or know how to do, the change.
My other favourite change is the 'db Spin Change', also by Dan and Dave, as it gives the illusion that there is only one card throughout the whole change. It really does look like there is only one card involved. It really looks like half the card changes as you spin, and then the other when you spread the cards. This makes the spectator think that the card actually morphs, not changes into another.