Though we can't yet see the real costumes for Scarlet Witch and Quicksilver, Marvel is giving us a sneak peek with some concept art. Much as the art of museums gives us a sneak peek at naked people before we're allowed to see those for real.
As you can see, for her Avengers: Age of Ultron role, it seems Elizabeth Olsen will trade out Scarlet Witch's traditional one-piece swimsuit for the scarlet of a red, collared jacket. Otherwise, she'll just wear some tattered old dress and some torn up tights. They'll probably just get dirty anyway. It's only practical.
Aaron Taylor-Johnson's Quicksilver, meanwhile, will seemingly hold on to his character's baby blue costume history, only now he'll also have all the standard little textures and sections that let us known this is a very serious baby blue costume. He can't do the collared jacket thing, because then it would look like he's wearing those blue pajamas every man in old sitcoms wore, and that would not be as serious of a baby blue costume.