I went to go see the new belt, and you are right about it - it looks more bronze than the old belts from five years ago. I can't recall when they got rid of the style of the longstanding belt, like the one Georges St-Pierre had at UFC 167.
The belts at the press conferences are not the actual belts they give to the champions, but I would assume they are made from the same materials. They are just used at the press conferences for aesthetic purposes, and probably in case athletes pack them away or forget to bring them.
As for DC...I think he can still fight for two more years for sure, but beating Jon Jones would not be easy. I also don't think DC wants to fight Jones again. I seem to recall DC vacating the belt as soon as Jones put his name in the USADA pool or something like that. So...I don't think that fight would happen - but it is possible.