Kind of doubt Marvel would be that sloppy in their work. I think it's probably intentional on their part. It's either some symbolism for the film or it's actually what CA's shield will look like for part of the film.
What makes more sense from a metaphorical POV:
a) The poster is of Cap's shield with the paint scarred and stripped away from the toughest battle(s) he's yet faced. Gone are his simple ideals about America, and he's having to adjust to an America he may no longer believe in, and that may no longer believe in him. Yet beneath it all remains the solid vibranium core, unbreakable like Steve Rogers himself.
b) Well, it turns out that SHIELD decided to paint over Cap's red white and blue shield with silver paint for some utterly inexplicable reason. ("Stealth?" bwahahahaha
) Only, it's not really paint anyway; it's clearly metal. And in order for this theory to work, there would necessarily be at least *two* levels of "paint" that are stripped away, including the 1940s original....in any event, looking past the factual inaccuracies of this theory, what's the metaphor supposed to represent? That if you strip off Cap's, uh, "shiny" exterior, there's a half-assed red white and blue --- well, mostly blue, with a little bit of red, and no visible white, and --- well....
Like I said: it's not that hard to figure out, people. The message in (a) is simple, direct, and poignant. Whatever layering issues are present in the poster are simple photoshop errors.
I think Superman had the disadvantage of not being a Batman movie. Man of Steel had Nolan's name attached to it, but it didn't have a direct connection to the Batman movies like all the Marvel movies have with each other.
HIGH-RES ASAP!