It was interesting – and frustrating – to see D'Artagnan on a boat outside of Belle-Isle, trying desperately to save his friends, only to be thwarted at every point as officer pops up with a signed order from the King specifically prohibiting each action. By the end of the scene, D'Artagnan is livid, but his antagonist is the King, so he can't do much. Clearly, although D'Artagnan has always professed loyalty to the King, he disagrees with a number of royal opinions throughout the novel.
Since D'Artagnan and his comrades are firmly on Fouquet's side, it makes sense that they dislike Fouquet's enemy, Colbert. This minister to the King is out to get Fouquet locked up by any means possible: hook, crook, or incriminating documents. Colbert thus only indirectly serves as an antagonist to D'Artagnan and Aramis. By the end of the novel, with Fouquet safely shut up in jail, two Musketeers have made amends with their once enemy..