I'm aware that they changed the costume for fans, which bugs me. If the change doesn't serve some thematic purpose, I'm going to hate it, regardless of how faithful it is.
Pretty sure the suit does have green in it.
And The Avengers was what Whedon wanted it to be. And it's faithfulness actually pushed the film forward. They didn't just put Steve in the classic red and blue for no reason. Unless Webb wants purple in the costume, there's really no reason to have it other than making fans happy (the same fans who will inevitably find something else to hate).
Just to clarify, I'm not saying there always has to be some reason for a costume. Director's vision can be reason enough. But if it isn't what the director wants, and it doesn't hold the film back in anyway, then I don't see any reason to do it.