Lots of spoilers for Captain America: The Winter Soldier below. If you're interested in a discussion of the film but don't want a bunch of plot points given away, check out my review.
As Captain America: The Winter Soldier progresses, it becomes clear that something is not right at the Strategic Homeland Intervention Enforcement and Logistics Division (SHIELD). Before being felled by a sniper's bullet, Nick Fury (Samuel L. Jackson) had trouble accessing classified data on a project that would put in the air a fleet of helicarriers with the ability to kill anyone in the world at a moment's notice. Bleeding out in front of Steve Rogers' (Chris Evans) eyes, Fury warns the good captain to trust no one.
As the film progresses we discover that Fury was right to be concerned. Captain America and the Black Widow (Scarlett Johansson) discover that the Nazi scientists who comprise Hydra have infiltrated SHIELD. Indeed, they've been there from the very beginning: SHIELD's founders invited Hydra scientists onboard as a part of Operation Paperclip. Over the years they have exerted their influence, using strike teams and stealth missions ostensibly aimed at controlling terrorism and protecting freedom to upset the world order.
Don't worry, though. Hydra is only interested in world domination as a way of introducing order to the planet. The greatest freedom is the freedom from fear, we are told. As SHIELD's helicarriers prepare to launch, a computerized version of the Red Skull's righthand man Arnim Zola (Toby Jones) informs Cap and Widow that they will utilize a massive NSA-style program* that will identify troublemakers for elimination. Al Qaeda extremists, Stephen Strange, and the president of the United States are all on the kill list—and it is extensive.
One can't make a utopian omelette without breaking twenty million or so eggs, after all.
As all of this is going down, an interesting and subtle transformation takes place. As the film opens, Captain America is wearing an extremely dark navy—bordering on black—stealth suit with a dirty silver star. It's a harder-edged look than we saw in either Captain America: The First Avenger or The Avengers: His shield is still red, white, and blue, but even it looks a bit grimier, a little tarnished.
After it is revealed that he has been doing the work of sworn enemy Hydra all along, however, Cap ditches the stealthy duds. He needs a uniform if he's going to go to war, he says. So he stops by the Smithsonian and snags a snazzy old look:
"Clothes contribute an enormous amount to the style of the picture," famed helmer Sidney Lumet wrote in Making Movies. The point that directors Joe and Anthony Russo are trying to make here strikes me as relatively obvious: What Cap was doing before—black bag ops like rescuing SHIELD tankers from pirates—aren't just bad. They're un-American. Cap's sartorial selection reflects the mood of the film and helps separate him from the ugliness he and his friends have uncovered.
*I'm curious to see if anyone on the right gets half as worked up about this subplot as they did about Noah. The phrase "flipside of the same coin" is used to describe SHIELD and Hydra, for god's sake.