Lets say you have 2 red property cards and one of the wild property cards that can be used as part of any property set to make a complete color set. If another player uses the Deal Breaker action card to steal a color set, are they able to steal the color set that has that wild property card? And if so, after they steal it, does that wild card have to remain part of that color set they stole? Or can they now use that wild card however they please?
A wild card can be used to make a full set. The Deal Breaker card can be used to steal a full set. There is no restriction that Deal Breaker cards can't be used to steal full sets that contain wild cards. Finally, you can reorganize your own sets on your turn, and the rules explicitly state that wild cards can be swapped between different sets. There is no restriction that wild cards become locked into a particular set once played.
Note that the wild card in question must actually be part of the full set. You can't use the Deal Breaker card to take two red properties plus a wild card that's in a different set or in no set at all. All the properties must be organized into a full set to be a target for Deal Breaker. It can actually be advantageous to not form full sets even when you can, to avoid having it stolen by a Deal Breaker (although you run the risk of being targeted by cards that can steal from non-full sets).