Yeah I think the B&W stuff works wonderfully in setting up the trailer. General audiences aren't going to know what this trailer is when it starts playing : black and white, moody Euro-looking locales, serious voiceovers, some violence, and then...Judi Dench is seen...hang on, isn't she in those Bond films...waitaminute, did he just say "Double O"...? And then BAM, the gunbarrel hits and the trailer bursts into action.
The French will throw them for a loop too.