Hopefully Tony's main suit, The Mark III, stays the same appearance wise through the course of the films. I think the mainstream public has come to identify the character with that color scheme and suit. I think if the suit gains new abilities that's perfectly fine, but don't change the main suit that much. If he needs to use other suits, i.e. The Hulkbuster Armor to track down the Hulk, that's fine too for special occasions.